Cheat Sheet Blueprint
Packet / Part IV · Exam Lab
28

Cheat Sheet Blueprint

One page, double-sided · what to actually write
If you remember one thing

Definitions are already in your open book. Spend the page on what you cannot look up fast: formulas, decision rules, and the shape of diagrams.

One page, front and back, plus the textbook and a calculator. Handwrite it. The writing is most of the value; a sheet copied from someone else is worth almost nothing.

Side 1 · Micro

εD
%ΔQ ÷ %ΔP · >1 elastic, <1 inelastic
Slope of PPC
−opportunity cost of the horizontal good
Comp. adv.
lowest opportunity cost, not highest output
ToT range
must sit between the two opportunity costs
CS
under D, above P · PS above S, under P
DWL
triangle points at efficient Q, opens to actual Q
Incidence
inelastic side bears the tax
Spending rule
mux/Px = muy/Py
Budget line
intercepts I/P · slope −Px/Py
Firm
MR = MC · competitive ⇒ P = MC
Profit
(P − ATC) × q · MC cuts ATC at its min
Monopoly
MR same intercept, 2× slope · Q from MR=MC, P off D
Externality
neg ⇒ SMC > PMC, overproduce · pos ⇒ SMB > PMB, underproduce

Side 2 · Macro

Y
C + I + G + NX · ≈$30T, 340M people, ≈$88k pp
Real GDP
fix prices · CPI fix quantities
Convert $
$XA × (PB/PA)
Fisher
r = i − π
PV
F/(1+i)t · rates ↑ ⇒ PV ↓
MRP
MRPL = MPL × MR · hire until = W
PAE
(C̄ − cT + I + G + NX) + cY
Equilibrium
set PAE = Y and solve
Multiplier
1/(1 − c) · G is 1:1, T is ×c
Y* pieces
(N*/POP) × (Y*/N*) · K/N and T
Gap ⇒ π
Y>Y* ⇒ π ↑ · Y<Y* ⇒ π ↓
Reaction fn
r − r̄ = 0.5(π − π̄) · shift up ⇒ lower LR π
Open economy
NX = −NKI · S + NKI = I sets r*
r ↑
C, I, NX all fall · $ appreciates

Also worth the space

  • Thumbnail sketches of the six diagrams you find hardest — tiny, just axes and curve names. Recognition beats reconstruction under time pressure.
  • The tariff welfare table (CS, PS, revenue, DWL = d + f). It is fiddly and you will not want to rederive it.
  • Named studies with one-line findings: Card (Mariel, no wage effect, elastic demand), Autor–Dorn–Hanson (China shock, concentrated and persistent), Piketty–Saez (tax data, top shares), Benzarti (VAT asymmetry), Frankel–Romer (geography instrument), Hall–Jones (social infrastructure), Heckman (early childhood returns).

Exam-day sequence

  1. Read the whole exam first. Two minutes. You will spot which long question is cheapest.
  2. Budget by points. The midterm is 60 points in 60 minutes — a point a minute. The final is 60 points in 90 minutes, so you get about a minute and a half per point. Either way, a 4-point graph gets four to six minutes, not twelve.
  3. Draw before you write. The diagram usually generates the sentences.
  4. Label everything. Axes, curves, equilibria, shaded regions. This is free credit and the most commonly forfeited.
  5. Answer the question asked. If it says "briefly explain," two sentences. Edwards penalizes padding: less is more.
  6. Leave nothing blank. A named model and a correct direction earns partial credit almost every time.

If you only have one evening

Do Unit 25 end to end, then Units 26 and 27 under timed conditions. That is roughly three hours and it covers the highest-density scoring in the course. Then handwrite the cheat sheet above from memory, checking only what you cannot recall — the gaps you find are exactly what to review next.