Subject: General Aptitude · Chapter: Problems on Trains · Exam: · Marks: · Difficulty:
A train running at a certain speed crosses a stationary engine in 20 seconds. To find out the speed of the train, which of the following information is necessary?
(a)Only the length of the train
(b)Only the length of the engine
(c)Either the length of the train or the length of the engine
(d)Both the length of the train and the length of the engine
Answer
Answer (as printed): D
Explanation
Time taken by the train to cross a stationary engine $$=\frac{\text { (Length of train }+ \text { Length of engine })}{(\text { Speed of the train })}$$ $\Rightarrow \frac{\text { (Length of train }+ \text { Length of engine) }}{(\text { Speed of the train })}=20$ (given) Hence, to find the speed of the train, the length of the train and the length of the engine both must be known. ∴ The correct answer is (d).
Explanation as extracted from the printed page; notation may be imperfect.