A train speeds past a pole in 20 seconds and passes through a tunnel 500 m long in 40 seconds. Its length is :  Answers:
A) 200 m  B) 400 m  C) 500 m  D) 700 m  E) None of the above
Sol.
Let the length of the train be x metres and its speed be y m/sec. Then, x / y = 20 ⇒ y = x / 20
∴ (x + 500) / 40 = x / 20 ⇔ x = 500 m. Answer 500 m
<result>C</result>
A train speeds past a pole in 20 seconds and passes through a tunnel 500 m long in 40 seconds. Its length is :