Discussion of Question with ID = 021 under Problems-on-Trains

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Question

A train takes 3 hours less if its speed is increased by 2 km/hr. What is the normal speed if the distance is 12km?

A

2.

B

3.

C

5.

D

4.

Soln.
Ans: a

Let the normal speed be x km/hr. We have been given $12/x$ - $12/{x + 2}$ = 3. This translates to the quadratic equation $3x^2 + 6x - 24 = 0$, which can be solved to obtain x = 2 as the answer. If you don't want to solve the equation, then you can put each option into this equation and check that way. But this trick will work only if all the options have some numerical value.


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