5Dec19 SS Q42

42Given below is a question followed by three statements.
Identify the statement, which is/are necessary to answer the question. 'What is the speed of the train'?
(A) The train crosses another train running in opposite direction in 20 seconds
(B) The train crosses a platform of length 300 m in 30 seconds
(C) The train crosses a pole in 10 seconds
Choose the most appropriate option:

Option : C
Explanation :
Let the length of one train is 'l'
Then from statement (C);
Time to cross a pole = 10 sec
∴ Speed of the train = l/10 ...(i)
from statement (B),
Length of the plateform = 300m
and time to cross the platform = 30 sec.
∴ Speed of the train = (l + 300)/30 ...(ii)
From (i) and (ii) an here l/10 = (l + 300)/30
3l = l + 300 ⇒ l = 150m
∴ Speed of the train = l/10 = 150/10 = 15m/sec.
Hence, statement (B) and (C) are enough to given the answer

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