Problem: a train consists of 12 boggies , each boggy 15 metres long . the train crosses a telegraph post in 18 seconds . due to some problem , two boggies were detached . the train now crosses a telegraph post in
Rationale: "length of train = 12 × 15 = 180 m . then , speed of train = 180 ⁄ 18 = 10 m / s now , length of train = 10 × 15 = 150 m ∴ required time = 150 ⁄ 10 = 15 sec . answer c"
annotated_formula: divide(subtract(multiply(12, 15), 15), divide(multiply(12, 15), 18))