Question

What is the length of a running train?
I. The train crosses a man in 9 seconds.
II. The train crosses a 240 metre long platform in 24 seconds.

• A. I alone sufficient while II alone not sufficient to answer
• B. II alone sufficient while I alone not sufficient to answer
• C. Either I or II alone sufficient to answer
• D. Both I and II are not sufficient to answer
• E. Both I and II are necessary to answer

Answer 1

The correct option is E Both I and II are necessary to answer

Time taken by train to cross a man $=\frac{\text{Length of train}}{\text{Speed of train}}\Rightarrow Speed=\frac{l}{9}$ ...... (i)
Time taken by train to cross a platform $=\frac{\text{Length of train + Length of platform}}{\text{Speed of train}}\Rightarrow Speed=\frac{l+240}{24}$ ....... (ii)
From (i) and (ii), we get $\frac{l}{9}=\frac{l+240}{24}$
Thus, $l$ can be obtained. So both I and II are necessary to get the answer.
$\therefore$ The correct answer is (E)