Question

What is the speed of the train?
I. The train crosses a signal pole in 18 seconds.
II. The train crosses a platform of equal length in 36 seconds.
III. Length of the train is 330 metres.

• A. I and II ony
• B. II and III only
• C. I and III only
• D. III and either I or II only
• E. Any two of the three

Answer 1

The correct option is D III and either I or II only

Let the speed of the train x metres/sec.
Time taken to cross a signal pole $=\frac{\text{Length of the train}}{\text{Speed of the train}}$
Time taken to cross a platform $=\frac{\text{(Length of the train + Length of the Platform)}}{\text{Speed of the train}}$
Length of train = 330 m.
I and III give, $18=\frac{330}{x}\Rightarrow x=\frac{330}{18}m/sec=\frac{55}{3}m/sec$
II and III give, $36=\frac{2\times 330}{x}\Rightarrow x=\frac{660}{36}m/sec=\frac{55}{3}m/sec$
$\therefore$ Correct answer is (D).