Price Quantity M′ = 3.5 P′ = 4.5 M = 4.5 P = 3.5 Q 3.5 → 4.5 (avg 4.0) · P $4.50 → $3.50 (avg $4.00) %ΔQ = 1/4.0 = 25.0% · %ΔP = 1/4.0 = 25.0% e = 25.0% / 25.0% ≈ 1.00 — unit elastic: total revenue is at its peak.