A train passes by a lamp post at platform in 7 sec. and passes by the platform completely in 28 sec. If the length of the platform is 390m, then length of the train (in meters) is?
A. 120 m
B. 130 m
C. 140 m
D. 150 m
Answer: Option B
Solution (By Examveda Team)
Length of train$$ = \frac{{{\text{Length}}\,{\text{of}}\,{\text{the}}\,{\text{platform}}}}{{{\text{Difference}}\,{\text{in time}}}}$$ × (Time taken to cross a lamp post)
$$\eqalign{ & = \frac{{390}}{{28 - 7}} \times 7 \cr & = \frac{{390}}{{21}} \times 7 \cr & = \frac{{390}}{3} \cr & = 130\,{\text{m}} \cr} $$
Let, the length of the train X meter.
X/7=390+X/28
X=130