Two persons are walking beside a railway track at respective speeds of 2 and 4 km per hour in the&nbsp;same direction. A train came from behind them and crossed them in 90 and 100 seconds,&nbsp;respectively. The time, in seconds, taken by the train to cross an electric post is nearest to&nbsp;

CAT 2020 Question Paper | CAT Verbal Ability Slot 1

Question :

Two persons are walking beside a railway track at respective speeds of 2 and 4 km per hour in the same direction. A train came from behind them and crossed them in 90 and 100 seconds, respectively. The time, in seconds, taken by the train to cross an electric post is nearest to

Started 1 month ago by Shashank in

0 26

A.
78
B.
75
C.
82
D.
87

Option C is the correct answer.

Explanatory Answer

Assume length of Train as L and Original speed as S
To cross the first person (2 kmph) train needs 90 seconds at S-2 km/hr and to cross the second
person (2 kmph) train needs 100 seconds at S-4 km/hr
Speeds are inversely proportional to time
(S-2)/(S-4) = (100/90)
S = 22
(S-2) = L * 3600 / 90
L = 0.5 km

T = (0.5 * 3600) / 22 = 82 seconds