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.  Choose one:	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.
Explanation:   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)/Relative speed   18 = (180 + x)/Relative speed   Thus, even with I, II and III, the answer cannot be obtained.   Answer is (Even with I, II and III, the answer cannot be obtained.).
<result>E</result>
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.