(a) 15 : 45 and 40 : 120
Product of extreme terms = 15 × 120 = 1800
Product of middle terms = 45 × 40 = 1800
∴ Product of extreme terms = Product of middle terms
∴ 15, 45, 40, and 120 are in proportion.
(b) 33 : 121 and 9 : 96
Product of extreme terms = 33 × 96 = 3168
Product of middle terms = 121 × 9 = 1089
∴ Product of extreme terms ≠ Product of middle terms
∴ 33, 121, 9, and 96 are not in proportion.
