Class 12 Economics Chapter 3 — Determination of Income and Employment (ASSEB, English Medium)
Welcome to HSLC Guru! This page presents complete English-medium notes, summary, textbook question answers, additional MCQs, fill in the blanks, true/false, glossary, and a formula table for Class 12 Economics Chapter 3 — Determination of Income and Employment, prepared strictly according to the ASSEB (Assam State School Education Board) syllabus. The chapter explains how the equilibrium level of national income and employment is determined in a two-sector and four-sector economy using Keynesian analysis. Important formulae such as the consumption function, marginal propensity to consume, investment multiplier, and concepts like paradox of thrift, deflationary gap and inflationary gap are explained in simple language with worked-out numerical problems.
Chapter Summary
In macroeconomics, the determination of income and employment is studied through two important concepts — ex-ante (planned/expected) and ex-post (actual/realised) values. Ex-ante refers to the values of variables such as consumption, saving and investment that economic agents plan to make in a given period. Ex-post refers to what is actually realised after the period ends. Equilibrium in the economy is reached when ex-ante aggregate demand equals ex-ante aggregate supply, that is, when planned spending matches planned output.
Aggregate Demand (AD) is the total demand for final goods and services in the economy in a given year. It has four components: private consumption expenditure (C), private investment expenditure (I), government expenditure (G), and net exports (NX = Exports − Imports). Therefore, AD = C + I + G + (X − M). Aggregate Supply (AS) is the total value of final goods and services produced in the economy during a year, which equals total national income (Y). The consumption function shows the relation between consumption and income and is written as C = c̄ + cY, where c̄ is autonomous consumption (consumption at zero income) and c is the marginal propensity to consume.
The Marginal Propensity to Consume (MPC) is the change in consumption per unit change in income (MPC = ΔC/ΔY) and lies between 0 and 1. The Average Propensity to Consume (APC) is total consumption divided by total income (APC = C/Y). The Marginal Propensity to Save (MPS) equals 1 − MPC, since every additional rupee of income is either consumed or saved. The investment multiplier (k) measures by how many times national income increases due to a unit increase in investment, given by k = 1/(1 − MPC) = 1/MPS. A higher MPC means a larger multiplier and a stronger expansionary effect.
Equilibrium income in a two-sector economy is determined where AS = AD or, equivalently, where planned saving equals planned investment (S = I). The paradox of thrift states that if all people in a society try to save more, total saving in the economy may actually fall because higher saving lowers consumption, demand and income. A deflationary (recessionary) gap occurs when aggregate demand falls short of the level needed for full-employment output, leading to unemployment. An inflationary gap occurs when aggregate demand exceeds full-employment output, causing prices to rise. Full-employment income is the level of national income at which all factors of production, especially labour, are fully employed.
Textbook Questions and Answers
A. Very Short Answer Questions (1 Mark)
Q1. What is meant by aggregate demand?
Answer: Aggregate demand is the total demand for final goods and services in an economy during a given period of time. It is the sum of consumption (C), investment (I), government expenditure (G) and net exports (X − M).
Q2. Define ex-ante and ex-post.
Answer: Ex-ante refers to the planned or desired values of economic variables (such as planned consumption or investment), while ex-post refers to the actual or realised values of those variables after the period is over.
Q3. Write the formula of consumption function.
Answer: The consumption function is C = c̄ + cY, where c̄ is autonomous consumption, c is the marginal propensity to consume and Y is the level of income.
Q4. What is the value range of MPC?
Answer: The value of marginal propensity to consume (MPC) lies between 0 and 1, that is, 0 < MPC < 1.
Q5. Write the formula of investment multiplier.
Answer: The investment multiplier is k = 1 / (1 − MPC) = 1 / MPS, where MPC is the marginal propensity to consume and MPS is the marginal propensity to save.
Q6. What is autonomous consumption?
Answer: Autonomous consumption (c̄) is that portion of consumption expenditure which does not depend on the level of income. It exists even when income is zero and is financed through past savings or borrowings.
Q7. Define paradox of thrift.
Answer: The paradox of thrift states that when every household in an economy tries to save more, aggregate saving in the economy may actually fall because higher saving leads to lower consumption, lower demand and lower income.
Q8. What is full-employment income?
Answer: Full-employment income is the level of national income at which all factors of production, especially labour, are fully employed and there is no involuntary unemployment in the economy.
Q9. Define marginal propensity to save (MPS).
Answer: Marginal propensity to save is the ratio of change in saving to change in income, MPS = ΔS/ΔY. It always equals 1 − MPC.
Q10. What is meant by deflationary gap?
Answer: A deflationary gap is the amount by which aggregate demand falls short of the aggregate demand required to maintain full-employment level of income. It causes unemployment and falling prices.
B. Short Answer Questions (2–3 Marks)
Q1. Distinguish between ex-ante and ex-post.
Answer: Ex-ante values are the planned, desired or intended values of economic variables for a future period (for example, planned investment or planned saving). Ex-post values are the actual realised values after the period is over. Equilibrium in the economy occurs when ex-ante demand equals ex-ante supply, but ex-post saving is always equal to ex-post investment as a matter of accounting identity.
Q2. What are the components of aggregate demand in a four-sector economy?
Answer: In a four-sector economy, aggregate demand consists of: (i) private consumption expenditure (C) by households, (ii) private investment expenditure (I) by firms, (iii) government expenditure (G) on goods and services, and (iv) net exports (NX), which equals exports minus imports (X − M). Hence, AD = C + I + G + (X − M).
Q3. Distinguish between APC and MPC.
Answer: APC (Average Propensity to Consume) is the ratio of total consumption to total income, APC = C/Y. MPC (Marginal Propensity to Consume) is the ratio of change in consumption to change in income, MPC = ΔC/ΔY. APC may be greater than 1 at very low income levels, but MPC always lies between 0 and 1. APC declines as income rises, while MPC is generally constant in the short run.
Q4. Explain the relationship between MPC and the multiplier.
Answer: The investment multiplier (k) is directly related to MPC. The formula k = 1/(1 − MPC) shows that the higher the MPC, the larger the multiplier. For example, if MPC = 0.5, k = 2; if MPC = 0.8, k = 5. A higher MPC means people spend a larger part of their additional income, which keeps the chain of income generation going for longer, producing a larger total increase in income from a given rise in investment.
Q5. Distinguish between deflationary gap and inflationary gap.
Answer: A deflationary gap is the shortfall of aggregate demand below the level needed for full-employment equilibrium, leading to unemployment and falling prices. An inflationary gap is the excess of aggregate demand over the full-employment level of output, which creates upward pressure on prices because supply cannot rise further. Deflationary gap requires expansionary policy (more spending, lower taxes), while inflationary gap requires contractionary policy.
Q6. What is paradox of thrift? Why does it occur?
Answer: The paradox of thrift refers to the situation where the attempt by every individual to save more leads to a fall in total saving of the economy. It occurs because higher saving means lower consumption demand, which reduces aggregate demand, output, employment and income. Lower income means people are unable to save more, and aggregate saving may fall back to or below the original level.
Q7. Write a short note on autonomous and induced consumption.
Answer: Autonomous consumption (c̄) is the part of consumption expenditure that does not depend on the level of income; it represents the minimum consumption required for survival even at zero income and is met from past savings or borrowings. Induced consumption is the part of consumption that varies directly with income and is given by cY in the consumption function C = c̄ + cY. As income rises, induced consumption rises but autonomous consumption remains unchanged.
Q8. If MPC = 0.6, find MPS and the value of investment multiplier.
Answer: Given MPC = 0.6.
MPS = 1 − MPC = 1 − 0.6 = 0.4.
Investment multiplier, k = 1/(1 − MPC) = 1/0.4 = 2.5.
Q9. Why does MPC lie between 0 and 1?
Answer: When income rises by one unit, people use a part of it for consumption and save the rest. They never consume more than the additional income (which would mean MPC > 1) nor do they save the entire additional income (which would mean MPC = 0). Hence the marginal propensity to consume must be a positive fraction lying strictly between 0 and 1, that is, 0 < MPC < 1.
C. Long Answer Questions (5–6 Marks)
Q1. Explain the determination of equilibrium income in a two-sector economy using the AD–AS approach.
Answer: In a two-sector economy with only households and firms, aggregate demand (AD) consists of consumption (C) and investment (I), so AD = C + I. Aggregate supply (AS) equals national income (Y). Equilibrium income is determined where AS = AD, i.e., Y = C + I. Substituting the consumption function C = c̄ + cY, we get Y = c̄ + cY + I, which gives Y(1 − c) = c̄ + I, hence the equilibrium income is:
Y = (c̄ + I) / (1 − c)
If AD > AS, firms find their inventories falling and they raise output until equilibrium is restored. If AD < AS, inventories pile up and firms reduce output. The same equilibrium can also be expressed as planned saving = planned investment (S = I), since in this model every rupee of income is either consumed or saved.
Q2. Explain the concept of investment multiplier with a numerical example.
Answer: The investment multiplier (k) measures the number of times by which the equilibrium income increases due to a unit increase in investment. It is given by k = ΔY/ΔI = 1/(1 − MPC) = 1/MPS.
Example: Suppose MPC = 0.8 and the increase in investment is ₹100 crore.
Then, k = 1/(1 − 0.8) = 1/0.2 = 5.
Therefore, increase in income, ΔY = k × ΔI = 5 × 100 = ₹500 crore.
This happens because the initial ₹100 crore investment becomes income for some people, who spend 80% (₹80 crore), which becomes income for others, who again spend 80% of it (₹64 crore), and so on. The successive rounds of spending add up to a total income increase of ₹500 crore.
Q3. In an economy, autonomous consumption is ₹200 crore, MPC = 0.75 and autonomous investment is ₹300 crore. Calculate (i) the equilibrium level of income, (ii) value of multiplier, and (iii) consumption at equilibrium.
Answer: Given: c̄ = 200, c = MPC = 0.75, I = 300.
(i) Equilibrium income, Y = (c̄ + I)/(1 − c) = (200 + 300)/(1 − 0.75) = 500/0.25 = ₹2000 crore.
(ii) Investment multiplier, k = 1/(1 − MPC) = 1/0.25 = 4.
(iii) Consumption, C = c̄ + cY = 200 + 0.75 × 2000 = 200 + 1500 = ₹1700 crore.
Check: Y = C + I → 1700 + 300 = ₹2000 crore. ✓
Q4. Explain the paradox of thrift with the help of an example.
Answer: The paradox of thrift, propounded by J. M. Keynes, states that an increase in the desire to save by all households simultaneously may reduce the total saving of the economy. Suppose initially equilibrium income is ₹1000 crore with consumption ₹800 crore and saving ₹200 crore. Now if all households decide to save more (say, MPS rises from 0.2 to 0.3), consumption falls. Lower consumption reduces aggregate demand. Firms cut production, employment and income. In the new equilibrium, income is lower, and total saving (which equals investment) may be the same or even smaller than before. Thus, individual virtue of thrift becomes a social vice. The paradox shows that saving is good for an individual but harmful for the economy when practised collectively in conditions of less than full employment.
Q5. Explain the meaning of deflationary gap and inflationary gap with diagrams (description).
Answer: The deflationary gap is the amount by which actual aggregate demand falls short of the aggregate demand required to maintain full-employment equilibrium. Diagrammatically, on the AD–Y graph, the AD curve cuts the 45° line at a level of income below the full-employment income (Yf). The vertical distance between the AD line at Yf and the 45° line at Yf is the deflationary gap. It causes unemployment, fall in prices and recession. The inflationary gap is the excess of actual aggregate demand over the aggregate demand needed to maintain full-employment equilibrium. The AD curve cuts the 45° line at a level above Yf, but since output cannot rise beyond Yf, the excess demand only pushes up prices. The vertical distance between AD at Yf and the 45° line at Yf is the inflationary gap. It causes inflation. To close the deflationary gap, government should increase its spending or reduce taxes; to close the inflationary gap, it should reduce spending or raise taxes.
Q6. An economy is in equilibrium at Y = ₹4000 crore. MPC = 0.75 and autonomous investment is ₹500 crore. (i) Find autonomous consumption. (ii) If investment rises by ₹200 crore, find the new equilibrium income.
Answer: Given Y = 4000, c = 0.75, I = 500.
(i) Y = c̄ + cY + I → 4000 = c̄ + 0.75 × 4000 + 500 → 4000 = c̄ + 3000 + 500 → c̄ = ₹500 crore.
(ii) Multiplier k = 1/(1 − 0.75) = 4. Increase in income = 4 × 200 = ₹800 crore. New equilibrium income = 4000 + 800 = ₹4800 crore.
Q7. Explain how excess demand and deficient demand affect equilibrium income.
Answer: Excess demand exists when planned aggregate demand is greater than aggregate supply at the full-employment level of income. As all factors are already fully employed, output cannot rise, so the excess demand only pushes the general price level up — this is the inflationary situation. Deficient demand exists when planned aggregate demand is less than aggregate supply at the full-employment level. Firms find inventories piling up, so they reduce output and employment, leading to unemployment, lower incomes and falling prices — this is the deflationary situation. To correct excess demand, the government should follow contractionary fiscal and monetary policies (raising taxes, reducing government spending, raising interest rates and CRR). To correct deficient demand, expansionary policies are needed (lowering taxes, raising government spending, reducing interest rates and CRR).
Additional Multiple Choice Questions (MCQs)
Q1. Aggregate demand in a four-sector economy is equal to —
(a) C + I (b) C + I + G (c) C + I + G + (X − M) (d) C + S
Answer: (c) C + I + G + (X − M)
Q2. If MPC = 0.8, the value of multiplier is —
(a) 2 (b) 4 (c) 5 (d) 10
Answer: (c) 5
Q3. The relationship between MPC and MPS is —
(a) MPC + MPS = 0 (b) MPC + MPS = 1 (c) MPC − MPS = 1 (d) MPC × MPS = 1
Answer: (b) MPC + MPS = 1
Q4. The consumption function is written as —
(a) C = c̄ − cY (b) C = c̄ + cY (c) C = cY − c̄ (d) C = c̄ × Y
Answer: (b) C = c̄ + cY
Q5. Equilibrium income is determined where —
(a) AS > AD (b) AS = AD (c) AS < AD (d) None of these
Answer: (b) AS = AD
Q6. The minimum value of MPC is —
(a) −1 (b) 0 (c) 0.5 (d) 1
Answer: (b) 0
Q7. Inflationary gap arises when —
(a) AD < AS at full employment (b) AD = AS at full employment (c) AD > AS at full employment (d) AD = 0
Answer: (c) AD > AS at full employment
Q8. If MPS = 0.25, the value of multiplier is —
(a) 2 (b) 3 (c) 4 (d) 5
Answer: (c) 4
Q9. Ex-post saving is always equal to —
(a) Ex-ante saving (b) Ex-ante investment (c) Ex-post investment (d) Consumption
Answer: (c) Ex-post investment
Q10. The paradox of thrift is associated with the work of —
(a) Adam Smith (b) David Ricardo (c) J. M. Keynes (d) A. C. Pigou
Answer: (c) J. M. Keynes
Q11. The slope of the consumption function C = c̄ + cY represents —
(a) Autonomous consumption (b) MPC (c) APC (d) MPS
Answer: (b) MPC
Q12. If autonomous investment is ₹400 crore, MPC = 0.5 and autonomous consumption is ₹100 crore, equilibrium income equals —
(a) ₹500 crore (b) ₹800 crore (c) ₹1000 crore (d) ₹2000 crore
Answer: (c) ₹1000 crore [Y = (100 + 400)/(1 − 0.5) = 500/0.5 = 1000]
Fill in the Blanks
Q1. The total demand for final goods and services in an economy is called __________.
Answer: aggregate demand
Q2. The investment multiplier is given by k = 1 / (__________).
Answer: 1 − MPC
Q3. The sum of MPC and MPS is always equal to __________.
Answer: 1 (one)
Q4. Consumption that does not depend on income is called __________ consumption.
Answer: autonomous
Q5. When AD exceeds AS at full-employment level, an __________ gap arises.
Answer: inflationary
True / False
Q1. The value of MPC is always greater than 1. — False (MPC lies between 0 and 1.)
Q2. Ex-post saving is always equal to ex-post investment. — True
Q3. If MPC = 0.5, the value of investment multiplier is 2. — True
Q4. Deflationary gap leads to rise in prices and full employment. — False (It causes unemployment and falling prices.)
Q5. Paradox of thrift means individual saving harms the saver. — False (It means collective saving may reduce aggregate saving in the economy.)
Glossary
| Term | Meaning |
|---|---|
| Ex-ante | Planned or expected values of variables before the period. |
| Ex-post | Actual or realised values of variables after the period. |
| Aggregate Demand (AD) | Total demand for final goods and services: C + I + G + (X − M). |
| Aggregate Supply (AS) | Total value of final goods and services produced; equals national income (Y). |
| Consumption Function | Functional relation between consumption and income: C = c̄ + cY. |
| Autonomous Consumption (c̄) | Consumption that is independent of income. |
| MPC | Marginal Propensity to Consume = ΔC/ΔY; lies between 0 and 1. |
| APC | Average Propensity to Consume = C/Y. |
| MPS | Marginal Propensity to Save = ΔS/ΔY = 1 − MPC. |
| Investment Multiplier (k) | Ratio of change in income to change in investment; k = 1/(1 − MPC). |
| Equilibrium Income | Level of income at which AS = AD or S = I. |
| Paradox of Thrift | Higher desire to save may lower aggregate saving in the economy. |
| Deflationary Gap | Shortfall of AD below full-employment AD; causes unemployment. |
| Inflationary Gap | Excess of AD over full-employment AD; causes inflation. |
| Full-Employment Income | Level of income at which all factors of production are fully employed. |
Important Formulae
| Concept | Formula |
|---|---|
| Aggregate Demand (4-sector) | AD = C + I + G + (X − M) |
| Aggregate Supply | AS = Y (National Income) |
| Consumption Function | C = c̄ + cY |
| Saving Function | S = −c̄ + (1 − c)Y |
| APC | APC = C / Y |
| APS | APS = S / Y |
| MPC | MPC = ΔC / ΔY |
| MPS | MPS = ΔS / ΔY = 1 − MPC |
| Relation | APC + APS = 1; MPC + MPS = 1 |
| Equilibrium Condition (2-sector) | Y = C + I or S = I |
| Equilibrium Income | Y = (c̄ + I) / (1 − c) |
| Investment Multiplier | k = 1 / (1 − MPC) = 1 / MPS |
| Change in Income | ΔY = k × ΔI |
| Deflationary Gap | AD at Yf < required AD for full employment |
| Inflationary Gap | AD at Yf > required AD for full employment |
Saving Function and Equilibrium (Alternative Approach)
The saving function is derived from the consumption function. Since Y = C + S, we get S = Y − C = Y − (c̄ + cY) = −c̄ + (1 − c)Y. Here −c̄ is autonomous saving (negative because at zero income people dis-save by drawing down past savings), and (1 − c) is the marginal propensity to save (MPS). Equilibrium income may be obtained by equating planned saving with planned investment: S = I, that is, −c̄ + (1 − c)Y = I, which on solving yields the same result Y = (c̄ + I)/(1 − c). Both AS = AD and S = I approaches give identical equilibrium income — they are simply two ways of looking at the same condition.
Numerical Practice (Solved)
Problem: In an economy, the consumption function is C = 100 + 0.8Y and autonomous investment I = 200. Find: (i) equilibrium income, (ii) saving at equilibrium, (iii) value of multiplier, (iv) increase in income if investment rises to 250.
Solution:
(i) Y = (c̄ + I)/(1 − c) = (100 + 200)/(1 − 0.8) = 300/0.2 = ₹1500.
(ii) S = Y − C = 1500 − (100 + 0.8 × 1500) = 1500 − 1300 = ₹200. (Note S = I as expected.)
(iii) k = 1/(1 − 0.8) = 5.
(iv) ΔI = 250 − 200 = 50; ΔY = 5 × 50 = ₹250. New Y = 1500 + 250 = ₹1750.
Quick Revision Notes
- Aggregate demand and aggregate supply jointly determine the equilibrium level of income.
- In a two-sector economy, equilibrium occurs at AS = AD, equivalent to S = I.
- Consumption rises with income but less than proportionately, so MPC < 1.
- The investment multiplier amplifies any change in autonomous investment by k = 1/MPS.
- Excess demand at full employment is inflationary; deficient demand causes deflation and unemployment.
- Fiscal policy (taxes, government spending) and monetary policy (interest rate, CRR, SLR) are used to correct these gaps.
- The paradox of thrift highlights the difference between individual rationality and collective outcomes.
Important Diagrams (Description for Reference)
- Consumption Function: A straight upward-sloping line starting at c̄ on the vertical axis, with slope equal to MPC. It lies below the 45° line at high incomes and above at low incomes.
- Saving Function: A straight upward-sloping line starting at −c̄ on the vertical axis, with slope equal to MPS. It crosses the X-axis at the break-even level of income where S = 0.
- Equilibrium Income (AD–AS): Income on the horizontal axis, AD on the vertical axis. The 45° line represents AS = Y. The AD curve C + I (or C + I + G + NX) cuts the 45° line at the equilibrium income Y*.
- Deflationary Gap: AD curve lies below the 45° line at full-employment income Yf. The vertical gap is the deflationary gap.
- Inflationary Gap: AD curve lies above the 45° line at Yf. The vertical gap is the inflationary gap.
Worked Example: Multiplier Chain
Suppose autonomous investment increases by ₹1000 crore and MPC = 0.8. The successive rounds of induced spending generate the following increase in income:
| Round | Increase in Income (₹ crore) | Increase in Consumption at MPC = 0.8 |
|---|---|---|
| 1 | 1000 | 800 |
| 2 | 800 | 640 |
| 3 | 640 | 512 |
| 4 | 512 | 409.6 |
| … | … | … |
| Total (sum to infinity) | 5000 | 4000 |
Total increase in income = ΔI / (1 − MPC) = 1000 / 0.2 = ₹5000 crore. This confirms the multiplier value k = 5 for MPC = 0.8.
Conclusion: Chapter 3 — Determination of Income and Employment — forms the core of Keynesian macroeconomics. Mastering the consumption function, multiplier mechanism, and equilibrium condition (AS = AD or S = I) is essential for both theory and numerical questions in the ASSEB Class 12 Economics examination. Practise the worked-out problems and remember the formulae listed above for quick revision. Continue with HSLC Guru for more chapter-wise notes and solved exercises tailored to the ASSEB Class 12 syllabus.