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# [Smart Math] Time Speed Distance Problem 5

Here’s and example of a SMART MATH problem for TIME SPEED DISTANCE.

### Problem

Two trains travel in the same direction at 50 and 32 km/hr. A man in the slower train observes that it takes 15 seconds for the faster train to completely pass him. What is the length of the slower train?

1. 75 meters
2. 100 meters
3. 160 meters
4. 200 meters
5. 250 meters

### The Usual Method

Relative speed of the two trains = 50 – 32 = 18 km/hr.

18 km/hr = $18\times \frac{5}{18}$ = 5 m/s

Hence, length of the slower train = 5 x 15 = 75 meters

(Ans: 1)

Estimated Time to arrive at the answer = 30 seconds.

### Using Technique

Since Distance = speed x time,

The length of the train should be a multiple of both the speed and the time.

Time taken is known as 15 seconds. Hence, length of the slower train should be a multiple of 15. The only option which is a multiple of 15 is option ‘1’.

(Ans: 1)

Estimated Time to arrive at the answer = 5 seconds.

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## One reply on “[Smart Math] Time Speed Distance Problem 5”

This question seems to be wrong.

The answer that has been calculated is for the length of faster train, not for the slower train