[ \textYED = \frac%\Delta QD%\Delta Y ] Repack Annotation: YED > 1 = luxury (income elastic). 0 < YED < 1 = necessity.

Let’s break down the repack by topic. In the official booklet, micro formulas are scattered. In our repack, we group them into three clusters: Elasticities, Tax Burdens, and Cost Curves. 1.1 Elasticities (SL & HL) Original Booklet: [ \textPED = \frac%\Delta QD%\Delta P ] Repack Annotation: Use the midpoint formula for arc elasticity: (Q2-Q1)/((Q1+Q2)/2) ÷ (P2-P1)/((P1+P2)/2)

[ \textXED = \frac%\Delta QD \text of Good A%\Delta P \text of Good B ] Repack Annotation: XED positive → substitutes (Coke/Pepsi). XED negative → complements (Printers/Ink).

That is where the concept of a comes in.

Multiplier = 1 / (MPS + MPT + MPM). MPS = 1 – MPC = 0.25. k = 1 / (0.25 + 0.1 + 0.05) = 1 / 0.4 = 2.5. ΔGDP = 40M × 2.5 = $100 million. Question 3 (International) Export price index rises from 100 to 120. Import price index rises from 100 to 110. Calculate Terms of Trade.

Good luck, and may the elasticities be ever in your favor.