A train passes a signal pole in 12 seconds and crosses a 180 m long bridge in 21 seconds. How long is the train?

Explanation

1. 01

   The extra $21 - 12 = 9$ seconds are spent covering the bridge's 180 m.

2. 02

   Speed $= \frac{180}{9} = 20$ m/s.

3. 03

   Length = speed × pole time $= 20 \times 12 = 240$ m.