A train consists of 12 boggies, each boggy 15 metres long. The train crosses a telegraph post in 9 seconds. Due to some problem, one boggies were detached. The train now crosses a telegraph post in  Choose the correct option:
A) 18 sec
B) 12 sec
C) 15 sec
D) 8.25 sec
E) none of these

Rationale: "length of train = 12 ã — 15 = 180 m . then , speed of train = 180 â  „ 9 = 20 m / s now , length of train = 11 ã — 15 = 165 m â ˆ ´ required time = 165 â  „ 20 = 8.25 sec . answer d"
Answer: D