Discussion Forum



Each of the questions given below consists of two statements numbered I and II given below it. Please read the questions carefully and decide whether the data provided in the statement(s) is / are sufficient to answer the given question.

1)

Find the speed of the train whose length is $210$ metres ?

I. The train crosses another train of $300$ meters length running in opposite direction in $10$ seconds.

II. The train crosses another train running in the same direction at the speed of $60$ km/hr in $30$ seconds.


A) I alone sufficient while II alone not sufficient to answer

B) II alone sufficient while I alone not sufficient to answer

C) Either I or II alone sufficient to answer

D) Both I and II are not sufficient to answer

E) Both I and II are necessary to answer

Answer:

Option E

Explanation:

Time taken to cross the train, running in opposite directions $=\frac{\left(l_{1}+l_2\right)}{(u+v)}$ sec.

$\Rightarrow 10$ $=\frac{(210+300)}{(u+v)}$ $\Rightarrow u+v$ $=51$.

Time taken to cross the train, running in same direction $=\frac{\left(l_{1}+l_{2}\right)}{(u-v)}$ sec.

$\Rightarrow 30$ $=\frac{(210+300)}{\left(u-60\times\frac{5}{18}\right)}$ $\Rightarrow u$ $=\left(17+\frac{50}{3}\right)$ m/sec.

Thus, $u$ and $v$ can be obtained.

$\therefore$ Correct answer is (E).