Aggregate demand is the first half of the AD-AS model — the framework behind most questions in "National Income and Price Determination" (15%–20% of the CLEP exam). The multiplier arithmetic in this lesson is among the most reliably tested quantitative material on the exam: stems like "an increase in government spending of $X will increase real GDP by at most..." appear in the official sample questions.
Aggregate demand (AD) shows the total quantity of domestic goods and services demanded (real GDP) at each price level. Its components are exactly GDP's spenders:
AD = C + I + G + Xn
Axes matter: the vertical axis is the price level (PL) — think CPI — not "price"; the horizontal axis is real GDP (Y), not "quantity."
You cannot substitute away from all goods at once, so micro's substitution logic fails here. Three macro effects explain the slope — a lower price level raises the quantity of real output demanded because it:
All three are movements along AD — the price level caused them.
| Component | AD shifts right when… | AD shifts left when… |
|---|---|---|
| C | Consumer confidence or wealth rises (stock portfolios, home values); personal taxes cut | Confidence or wealth falls; personal taxes raised |
| I | Interest rates fall (from policy or markets); business optimism rises; business taxes cut | Rates rise; pessimism spreads |
| G | Government purchases increase | Government purchases decrease |
| Xn | Foreign incomes rise; domestic currency depreciates | Foreign recession; currency appreciates |
One subtlety: interest-rate changes caused by the price level are the slope mechanism (movement along); interest-rate changes from any other cause — central bank policy, loanable-funds events — shift AD. Ask why the rate moved.
Transfer payments and tax changes work through C (households spend part of the extra disposable income) — they are not government purchases, and the multiplier math treats them differently, as you'll see below.
[GRAPH: Aggregate Demand
X-axis: Real GDP (Y)
Y-axis: Price level (PL)
Curve 1: AD, downward-sloping, labeled AD₁
Reading: at PL = 110, real GDP demanded = $18T; at PL = 100, $19T —
a movement ALONG AD₁ (wealth, interest-rate, exchange-rate effects)
Shift: consumer confidence surges → C rises at EVERY price level → entire
curve shifts right to AD₂]
When households receive an extra dollar of income, they spend part and save part:
MPC = ΔC/Δincome MPS = ΔS/Δincome MPC + MPS = 1
Why spending multiplies: the government buys $100M of bridge repairs → construction workers earn $100M → with MPC = 0.8 they spend $80M → shopkeepers earn $80M and spend $64M → and so on. The geometric series sums to:
Spending multiplier = 1/MPS = 1/(1 − MPC)
With MPC = 0.8: multiplier = 1/0.2 = 5. A $100M spending increase raises real GDP by at most $500M. The same multiplier applies to any initial change in spending — a fall in business investment multiplies downward identically.
Tax multiplier = −MPC/MPS
Why smaller: a $100M tax cut doesn't inject $100M of spending — households save $20M of it (with MPC = 0.8), so only $80M enters round one. Result: −(0.8/0.2) = −4; a $100M tax cut raises GDP by at most $400M. Transfers work like negative taxes: same magnitude logic.
Raise G and taxes by the same $100M → +5(100) − 4(100) = +$100M. The balanced-budget multiplier is exactly 1: equal increases in spending and taxes still expand GDP by the initial change in G.
Worked example: MPC = 0.75. Spending multiplier = 1/0.25 = 4; tax multiplier = −0.75/0.25 = −3. To close a $300B output gap: new government purchases of 300/4 = $75B, or a tax cut of 300/3 = $100B. Tax cuts must always be larger to do the same job.
(Real-world multipliers are blunted by taxes, imports, and price-level rises. The formula gives the maximum — when a question says "at most," use it straight.)
1. D. Spending multiplier = 1/MPS = 1/(1 − MPC). A: multiplying the two propensities has no economic meaning — they sum to 1, not multiply to a multiplier. B: puts consumption, not saving, in the denominator. C: MPC/MPS is the tax multiplier's magnitude. E: 1 − MPC is just the MPS itself, not the multiplier.
Fix: Spending multiplier = 1 over the leakage rate: 1/MPS = 1/(1 − MPC).
2. B. The wealth (real-balances) effect: a lower price level makes money holdings buy more → consumption rises. A: micro substitution logic — invalid when all prices fall together. C: production costs belong to the supply curve. D: G is set by policy, not by the price level. E: the money supply is set by the central bank, not by the price level.
Fix: AD's slope = wealth + interest-rate + exchange-rate effects — never micro substitution.
3. B. The price level is the vertical-axis variable: its changes move you along AD. A: tax cuts shift AD through C. C: G is a direct shifter. D: optimism shifts AD through I. E: foreign incomes shift AD through Xn.
Fix: PL changes → slide along the curve; everything else that touches C, I, G, or Xn → shift.
4. A. Appreciation makes exports pricier abroad and imports cheaper at home → Xn falls → AD shifts left. B: cheaper imports reduce net exports — buying more foreign goods subtracts from AD. C: backwards — appreciation hurts export revenues. D: exchange rates hit the Xn component directly. E: exchange-rate events shift the curve; they do not change its slope.
Fix: Appreciation → Xn down → AD left; depreciation → Xn up → AD right.
5. E. Multiplier = 1/(1 − 0.9) = 1/0.1 = 10. A: that is the MPC itself. B: uses MPC/MPS (0.9/0.1) — the tax multiplier's magnitude. C: inverts, computing 1/0.9. D: a decimal slip (10 × 9).
Fix: Convert MPC to MPS first, then take 1/MPS.
6. C. Multiplier = 1/0.2 = 5; 5 × $50B = $250B. A: forgets to multiply at all. B: multiplies by the MPC once instead of the full series. D: uses a multiplier of 4 — the tax multiplier's magnitude. E: divides by the MPC instead of multiplying by the multiplier.
Fix: ΔGDP = multiplier × ΔG — compute the multiplier first, then scale.
7. D. Business-tax cuts raise I; more government purchases raise G — both push AD right. A: higher personal taxes push left, conflicting with the G increase. B: rising rates push left, conflicting with confidence. C: appreciation pushes left, conflicting with foreign incomes. E: falling stock prices push left, conflicting with falling rates.
Fix: For "unambiguous" combinations, sign each event separately; any conflict makes the net direction indeterminate.
8. E. Tax multiplier = −0.75/0.25 = −3; −3 × (+$60B) = −$180B. A: uses the spending multiplier's magnitude (4 × 60). B: sign error — a tax increase lowers GDP. C: multiplies by the MPC only. D: divides by the MPC instead of applying the multiplier.
Fix: ΔGDP = (−MPC/MPS) × ΔT — write the sign of ΔT explicitly before multiplying.
9. A. Balanced-budget multiplier = 1: +5(40) − 4(40) = 200 − 160 = +$40B. B: assumes full cancellation, forgetting that the two multipliers differ in size. C: adds the two effects' magnitudes without netting the tax drag. D: the spending effect alone. E: the tax effect alone, presented as the net.
Fix: Equal ΔG and ΔT still stimulate — the net effect equals the initial ΔG (multiplier of exactly 1).
10. C. Each round spends the MPC of the previous round: 10 → 6 → 3.6 → …; total = 10 × 1/(1 − 0.6) = $25M. A: ignores all induced consumption. B: rounds shrink geometrically; they never grow. D: $4M is the saved share of round one, and rounds shrink rather than repeat. E: mistakes the leakage for the process — spending continues at a diminishing rate.
Fix: The multiplier is a shrinking geometric series of respending — each round = MPC × the previous round.
11. B. Transfers are not purchases of goods or services; they raise disposable income, and the spending out of that income raises C. A: only direct government purchases of goods and services enter G. C: some leakage to imports exists, but the primary channel is C, and the claim being evaluated concerns G. D: the induced consumption plainly moves AD. E: deposits are saving — a leakage, not the mechanism.
Fix: Transfers and tax cuts enter AD only through C — one step removed from G, which is why they get the smaller multiplier.
12. A. Spending multiplier = 1/0.25 = 4, so 4 × $75B = $300B closes the gap; tax multiplier magnitude = 0.75/0.25 = 3, so a $75B tax cut yields at most $225B — short by $75B (a $100B cut would be needed). B: the tax multiplier is always smaller in magnitude. C: the spending figure does close the gap. D: reversed — the tax cut is the one that falls short. E: multipliers apply separately to their own tools; summing them is meaningless.
Fix: Same dollar figure, different tools, different results — tax changes always need to be larger than spending changes to move GDP equally.
1. D. Spending multiplier = 1/MPS = 1/(1 − MPC). A: multiplying the two propensities has no economic meaning — they sum to 1, not multiply to a multiplier. B: puts consumption, not saving, in the denominator. C: MPC/MPS is the tax multiplier's magnitude. E: 1 − MPC is just the MPS itself, not the multiplier. Fix: Spending multiplier = 1 over the leakage rate: 1/MPS = 1/(1 − MPC).
2. B. The wealth (real-balances) effect: a lower price level makes money holdings buy more → consumption rises. A: micro substitution logic — invalid when all prices fall together. C: production costs belong to the supply curve. D: G is set by policy, not by the price level. E: the money supply is set by the central bank, not by the price level. Fix: AD's slope = wealth + interest-rate + exchange-rate effects — never micro substitution.
3. B. The price level is the vertical-axis variable: its changes move you along AD. A: tax cuts shift AD through C. C: G is a direct shifter. D: optimism shifts AD through I. E: foreign incomes shift AD through Xn. Fix: PL changes → slide along the curve; everything else that touches C, I, G, or Xn → shift.
4. A. Appreciation makes exports pricier abroad and imports cheaper at home → Xn falls → AD shifts left. B: cheaper imports reduce net exports — buying more foreign goods subtracts from AD. C: backwards — appreciation hurts export revenues. D: exchange rates hit the Xn component directly. E: exchange-rate events shift the curve; they do not change its slope. Fix: Appreciation → Xn down → AD left; depreciation → Xn up → AD right.
5. E. Multiplier = 1/(1 − 0.9) = 1/0.1 = 10. A: that is the MPC itself. B: uses MPC/MPS (0.9/0.1) — the tax multiplier's magnitude. C: inverts, computing 1/0.9. D: a decimal slip (10 × 9). Fix: Convert MPC to MPS first, then take 1/MPS.
6. C. Multiplier = 1/0.2 = 5; 5 × $50B = $250B. A: forgets to multiply at all. B: multiplies by the MPC once instead of the full series. D: uses a multiplier of 4 — the tax multiplier's magnitude. E: divides by the MPC instead of multiplying by the multiplier. Fix: ΔGDP = multiplier × ΔG — compute the multiplier first, then scale.
7. D. Business-tax cuts raise I; more government purchases raise G — both push AD right. A: higher personal taxes push left, conflicting with the G increase. B: rising rates push left, conflicting with confidence. C: appreciation pushes left, conflicting with foreign incomes. E: falling stock prices push left, conflicting with falling rates. Fix: For "unambiguous" combinations, sign each event separately; any conflict makes the net direction indeterminate.
8. E. Tax multiplier = −0.75/0.25 = −3; −3 × (+$60B) = −$180B. A: uses the spending multiplier's magnitude (4 × 60). B: sign error — a tax increase lowers GDP. C: multiplies by the MPC only. D: divides by the MPC instead of applying the multiplier. Fix: ΔGDP = (−MPC/MPS) × ΔT — write the sign of ΔT explicitly before multiplying.
9. A. Balanced-budget multiplier = 1: +5(40) − 4(40) = 200 − 160 = +$40B. B: assumes full cancellation, forgetting that the two multipliers differ in size. C: adds the two effects' magnitudes without netting the tax drag. D: the spending effect alone. E: the tax effect alone, presented as the net. Fix: Equal ΔG and ΔT still stimulate — the net effect equals the initial ΔG (multiplier of exactly 1).
10. C. Each round spends the MPC of the previous round: 10 → 6 → 3.6 → …; total = 10 × 1/(1 − 0.6) = $25M. A: ignores all induced consumption. B: rounds shrink geometrically; they never grow. D: $4M is the saved share of round one, and rounds shrink rather than repeat. E: mistakes the leakage for the process — spending continues at a diminishing rate. Fix: The multiplier is a shrinking geometric series of respending — each round = MPC × the previous round.
11. B. Transfers are not purchases of goods or services; they raise disposable income, and the spending out of that income raises C. A: only direct government purchases of goods and services enter G. C: some leakage to imports exists, but the primary channel is C, and the claim being evaluated concerns G. D: the induced consumption plainly moves AD. E: deposits are saving — a leakage, not the mechanism. Fix: Transfers and tax cuts enter AD only through C — one step removed from G, which is why they get the smaller multiplier.
12. A. Spending multiplier = 1/0.25 = 4, so 4 × $75B = $300B closes the gap; tax multiplier magnitude = 0.75/0.25 = 3, so a $75B tax cut yields at most $225B — short by $75B (a $100B cut would be needed). B: the tax multiplier is always smaller in magnitude. C: the spending figure does close the gap. D: reversed — the tax cut is the one that falls short. E: multipliers apply separately to their own tools; summing them is meaningless. Fix: Same dollar figure, different tools, different results — tax changes always need to be larger than spending changes to move GDP equally.