Theory of Income and Employment: ISC Class 12 Economics Notes and Numericals

What Theory of Income and Employment is about

Weightage: Theory of Income and Employment is part of the syllabus unit that carries 8 of the 80 theory marks. Questions on it can appear in any section of the paper.Source: CISCE ISC Economics syllabus, examination year 2027, distribution of marks

Key concepts

Ex-ante and ex-post demand; aggregate demand and its components

Ex-ante (planned) demand: the aggregate of planned expenditure on final goods and services by all sectors of the economy during a period, at a given level of income. Ex-post (actual/realised): what was actually spent at the end of the period. Equilibrium is defined in ex-ante terms; ex-post saving and investment are always equal.

Effective demand is the level of AD at which it equals AS; it determines equilibrium output and employment.

Components of AD:

• Household consumption (C): depends mainly on income.
• Investment (I): by firms on capital goods and inventories; in the simple model, autonomous investment (independent of income; horizontal line) as against induced investment (which rises with income).
• Government expenditure (G).
• Net exports (X − M).

Worked example

Suppose households plan to spend ₹800 crore, firms plan to invest ₹200 crore and the government plans ₹150 crore, with exports ₹60 crore and imports ₹90 crore. Find aggregate demand. [1 mark]

Try it first, then show the solutionSolution

1. AD = C + I + G + (X − M) = 800 + 200 + 150 + (60 − 90).

Answer: ₹1,120 crore.

Consumption and saving functions; APC, MPC, APS, MPS

Consumption function: C = a + bY, where a > 0 is autonomous consumption and b = MPC (0 < b < 1). The consumption curve starts from a point above the origin on the Y-axis (it never passes through the origin).

Saving function: S = Y − C = −a + (1 − b)Y; the saving curve starts below the origin (dissaving at zero income).

• APC = C/Y; APS = S/Y; APC + APS = 1 (so APS = 1 − APC).
• MPC = ΔC/ΔY; MPS = ΔS/ΔY; MPC + MPS = 1.
• APC can exceed 1 at low incomes (dissaving); MPC lies between 0 and 1.
• Break-even point: C = Y, S = 0.

Worked example

Suppose C = 100 + 0.8Y (₹ crore). Prepare the consumption and saving schedule for Y = 0, 500, 1,000 and 1,500 and find APC, APS and the break-even income. [3 marks]

Income Y (₹ crore)	Consumption C	Saving S	APC	APS
0	100	−100	—	—
500	500	0	1	0
1,000	900	100	0.90	0.10
1,500	1,300	200	0.87	0.13

Try it first, then show the solutionSolution

1. C = 100 + 0.8Y; S = Y − C.
2. Break-even where C = Y: 100 + 0.8Y = Y → Y = 500.
3. APC + APS = 1 at every income; MPC = 0.8, MPS = 0.2 throughout.

Answer: Break-even at ₹500 crore; APC falls as income rises.

Determination of equilibrium income

Two approaches (two-sector model):

1. AD = AS: AD (C + I) is plotted against income; AS is the 45° line (Y). Equilibrium at their intersection: planned spending equals output.
2. S = I: planned saving equals planned investment.

If AD > AS (I > S): unplanned fall in inventories, so firms raise output and income rises. If AD < AS (S > I): unsold stocks pile up, so output and income fall.

With C = a + bY and autonomous investment I: Y = (a + I) ÷ (1 − b).

The equilibrium is not necessarily at full employment: it may be below (unemployment equilibrium) or above.

Worked example

Suppose C = 100 + 0.8Y and I = ₹200 crore. Find equilibrium income and show that S = I there. [2 marks]

Try it first, then show the solutionSolution

1. Y = (100 + 200) ÷ 0.2 = ₹1,500 crore.
2. S = −100 + 0.2 × 1,500 = ₹200 crore = I.

Answer: ₹1,500 crore; S = I = ₹200 crore.

Investment multiplier

Meaning: the investment multiplier (k) is the number of times by which income increases as a result of an increase in investment: k = ΔY ÷ ΔI. An initial rise in investment raises income by a larger amount.

Mechanism: an extra ₹100 crore of investment becomes income for workers and suppliers; they spend a part (MPC) of it, which becomes income for others, who again spend part of it, and so on. The total rise in income is the sum of these rounds: ΔY = ΔI (1 + b + b² + …) = ΔI ÷ (1 − b).

Relation with MPC: k = 1 ÷ (1 − MPC) = 1 ÷ MPS. The higher the MPC, the larger the multiplier (direct relation). Range: k = 1 when MPC = 0; k = ∞ when MPC = 1.

Diagram: AD shifts up by ΔI; the new equilibrium on the 45° line shows ΔY > ΔI.

Worked example

Suppose national income rises from ₹800 crore to ₹1,200 crore and consumption from ₹600 crore to ₹900 crore. Calculate MPC and the investment multiplier. [2 marks]

Try it first, then show the solutionSolution

1. MPC = ΔC ÷ ΔY = 300 ÷ 400 = 0.75.
2. k = 1 ÷ (1 − 0.75) = 4.

Answer: MPC 0.75; multiplier 4.

Full employment; excess and deficient demand

Full employment: a situation where all those who are able and willing to work at the existing wage rate get work. Voluntary and frictional unemployment may still exist; involuntary unemployment does not.

Excess demand: AD exceeds AS at the full-employment level of output. The gap is the inflationary gap. Since output cannot rise further, the result is inflation (rise in prices), with no rise in output or employment.

Deficient demand: AD falls short of AS at the full-employment output. The gap is the deflationary gap. Result: fall in output, involuntary unemployment, falling prices.

Both gaps are measured vertically at the full-employment level of income. Inflation types: demand-pull (excess AD) and cost-push (rise in costs such as wages or raw material prices pushing prices up; diagrams not required).

Worked example

Suppose full-employment output is ₹5,000 crore but AD at that output is only ₹4,600 crore. What is the gap and what does it cause? [2 marks]

Try it first, then show the solutionSolution

1. AD < AS at full employment by ₹400 crore: a deflationary gap.
2. Firms cannot sell all output; they cut production and jobs: involuntary unemployment.

Answer: Deflationary gap of ₹400 crore, causing unemployment.

Measures to correct excess and deficient demand

Measure	Excess demand (reduce AD)	Deficient demand (raise AD)
Bank rate / repo rate (monetary)	Raise	Lower
Cash reserve ratio, SLR	Raise	Lower
Open market operations	Sell securities	Buy securities
Margin requirements	Raise	Lower
Moral suasion / selective credit control	Restrict credit	Encourage credit
Taxes (fiscal)	Raise	Cut
Government expenditure	Reduce	Increase
Public borrowing	Increase (absorb purchasing power)	Reduce
Deficit financing	Reduce	Increase

Monetary measures act through the cost and availability of credit; fiscal measures act directly on income and spending.

Worked example

Suppose an economy faces an inflationary gap. Suggest one monetary and one fiscal measure and explain how each works. [2 marks]

Try it first, then show the solutionSolution

1. Monetary: raise the repo rate; loans become dearer, borrowing and spending fall.
2. Fiscal: cut government expenditure (or raise taxes); AD falls directly.

Answer: Higher repo rate; lower government spending.

Theory of Income and Employment in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Consumption and Saving Functions: APC, MPC, APS, MPS and the Break-Even Point
• Equilibrium Income and the Investment Multiplier
• Excess Demand and Deficient Demand: Gaps and Corrective Measures

Theory of Income and Employment: key facts

Aggregate demand

AD = C + I (two-sector); C + I + G + (X − M) (four-sector)

Consumption function

C = a + bY; S = −a + (1 − b)Y

Propensities

APC = C/Y; APS = S/Y; APC + APS = 1; MPC = ΔC/ΔY; MPS = ΔS/ΔY; MPC + MPS = 1

Equilibrium income

Y = (a + I) ÷ (1 − b), where AD = AS and S = I

Investment multiplier

k = ΔY ÷ ΔI = 1 ÷ (1 − MPC) = 1 ÷ MPS

How the board asks Theory of Income and Employment

The question patterns to expect, and the method that works for each.

Tricks to remember Theory of Income and Employment

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Ones that add to one

  APC + APS = 1 and MPC + MPS = 1: income is either spent or saved.

  Use it when: Finding missing propensities.

• Multiplier = 1/MPS

  The leak (saving) decides the size: smaller leak, bigger multiplier.

  Use it when: Multiplier numericals.

• Gaps live at full employment

  Measure inflationary and deflationary gaps vertically at the full-employment output only.

  Use it when: Gap diagrams.

Theory of Income and Employment: board-level solved questions

Ordered from board level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section C style)

Read the situation, then answer every part. In the board paper this is a 8-mark question split into 2 + 2 + 2 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Theory of Income and Employment

The slips examiners see most often, and what to write instead.

• ✗Mistake: Wrong formulas for MPC and multiplier

  CISCE examiners' comments, 2024: "Applied incorrect formulas for MPC and the multiplier"; CISCE examiners' comments, 2025: "Wrote the formula as 1/MPC instead of 1/(1−MPC)".

  ✓Do this: MPC = ΔC/ΔY; k = 1/(1 − MPC) = 1/MPS.

  Usually costs: 1-2 marks.

• ✗Mistake: Consumption curve through the origin

  CISCE examiners' comments, 2024: "Drew consumption curve passing through the origin"; "Drew consumption curve as a horizontal straight line"; "Missed labelling or labelled diagrams incorrectly".

  ✓Do this: Start the C curve at a positive intercept (autonomous consumption) and slope it upwards; label axes.

  Usually costs: 1 mark.

• ✗Mistake: Ex-ante demand without "aggregate"

  CISCE examiners' comments, 2024: "Did not explain the macro concept; terms 'sum-total' or 'aggregate' missing".

  ✓Do this: Write "aggregate planned expenditure of all sectors".

  Usually costs: 1 mark.

• ✗Mistake: Gap not linked to full employment

  CISCE examiners' comments, 2025: "Confused the deflationary gap with the inflationary gap"; "Defined the deflationary gap without reference to full employment".

  ✓Do this: Both gaps are measured at the full-employment output.

  Usually costs: 1 mark.

• ✗Mistake: Relations of propensities misstated

  CISCE examiners' comments, 2024: "Wrote APC + APS = Y instead of APC + APS = 1".

  ✓Do this: APC + APS = 1; MPC + MPS = 1.

  Usually costs: 1 mark.

Practice questions on Theory of Income and Employment

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQBoard level

   If MPC = 0.6, the investment multiplier is:
   (a) 1.67
   (b) 2.5
   (c) 0.4
   (d) 6

   Hint

   1/MPS.

   Answer

   (b) 2.5

2. Q2 · 1 mark · Very short answerBoard level

   Give one difference between autonomous and induced investment.

   Hint

   Relation to income.

   Answer

   Autonomous investment does not depend on income (horizontal curve); induced investment rises with income (upward-sloping curve).

3. Q3 · 1 mark · Very short answerHarder board level

   Define ex-ante aggregate demand.

   Hint

   Aggregate and planned.

   Answer

   The total planned expenditure on final goods and services by all sectors of the economy during a period, at a given level of income.

4. Q4 · 2 marks · Short answerHarder board level

   Income rises from ₹2,000 crore to ₹2,500 crore and saving from ₹400 crore to ₹500 crore. Find MPC and k.

   Hint

   MPS first.

   Answer

   MPS = 100 ÷ 500 = 0.2; MPC = 0.8; k = 5.

5. Q5 · 2 marks · Short answerHarder board level

   An increase in investment of ₹300 crore raises income by ₹1,200 crore. Find MPC.

   Hint

   k first.

   Answer

   k = 4 = 1/(1 − MPC); MPC = 0.75.

6. Q6 · 2 marks · Short answerBoard level

   Distinguish between inflationary gap and deflationary gap.

   Hint

   Full employment.

   Answer

   Inflationary: AD exceeds AS at full employment, causing a price rise. Deflationary: AD falls short of AS at full employment, causing unemployment.

7. Q7 · 2 marks · Short answerHOTS / competency

   Explain why an increase in output is not possible when there is excess demand.

   Hint

   Full employment.

   Answer

   At full employment all resources are already employed, so extra demand cannot be met by more output; it only raises prices.

8. Q8 · 2 marks · Short answerHOTS / competency

   Why can MPC never be greater than 1 in the simple model, though APC can?

   Hint

   Change versus level.

   Answer

   Out of an extra rupee of income, a household cannot spend more than the rupee (MPC ≤ 1); but at low incomes total consumption can exceed income through dissaving, so APC > 1.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Equilibrium condition (two-sector)?Show answer

   AD = AS, or planned S = planned I.

2. 2.Multiplier formula?Show answer

   k = 1/(1 − MPC) = 1/MPS.

3. 3.Where is the inflationary gap measured?Show answer

   At the full-employment level of output.

4. 4.APC + APS = ?Show answer

   1.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐C = a + bY; a = autonomous consumption; b = MPC.
• ☐APC + APS = 1; MPC + MPS = 1.
• ☐Y = (a + I)/(1 − b).
• ☐k = 1/MPS; higher MPC → higher k.
• ☐Inflationary gap: AD > AS at full employment; deflationary: AD < AS.
• ☐Fix excess demand: tighten money, raise taxes, cut spending.

Theory of Income and Employment: frequently asked questions