Question

What is the length of a running train P crossing another running train Q?
I. These two trains take 18 seconds to cross each other.
II. These trains are running in opposite directions.
III. The length of the train Q is 180 metres.

• A. I only
• B. II only
• C. III only
• D. All I, II and III are required
• E. Even with I, II and III, the answer cannot be obtained.

Answer 1

The correct option is E Even with I, II and III, the answer cannot be obtained.

Let the length of the train P be x metres.
II. These trains are running in opposite directions.
III. Length of the train Q is 180 m.
I. Time taken by P to cross Q $=\frac{(180+x)}{\text{Relative speed}}\Rightarrow 18=\frac{(180+x)}{\text{Relative speed}}$
Thus, even with I, II and III, the answer cannot be obtained.
$\therefore$ Correct answer is (E).