Trains Boats and Streams Practice Test 2 with solutions

Let the speed of the train = x m/second and length be y m
Time = $\frac{\mathrm{Distance}}{\mathrm{Speed}}$
4 = $\frac{\mathit{y}}{\mathit{x}}$
⇒ y = 4x ......(i)
When time is equal to 12 seconds,
12 = $\frac{\mathit{y}+100}{\mathit{x}}$
12x = y + 100
Using (i) we get
12x = 4x + 100
8x = 100
x = $\frac{100}{8}$ = $\frac{25}{4}$ = 6.25 m/seconds
y = 4 (6.25) = 25 m