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Problems on Trains - General Aptitude

Each of these questions is followed by three statements. You have to study the question and all the three statements given to decide whether any information provided in the statement(s) is redundant and can be dispensed with while answering the given question.
Q1:

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.

ANS: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 = (180 + x)      18 = (180 + x)
Relative speed Relative speed
Thus, even with I, II and III, the answer cannot be obtained.  Correct answer is (E).