Discussion

Explanation:

Both the person and the escalator are moving in the same direction. In this case, the relative speed would be Speed of (Man + Stairs).

We don’t know the speed of the escalator, so assume that to be e.

Let speed of P be 5a steps/sec and Q's is 3a steps/sec.

P is walking 50 steps and he does it in 50/5a = 10/a secs., but in this 10/a secs, even the escalator must have moved with speed "e". The length moved by it would be 10e/a.

So, we can say the total length is 50 + 10e/a (steps moved by P and the escalator helps P in reaching the top).

Similarly for Q we can write 40 + 40e/3a

Both are moving on the same escalator, hence total number of steps should be same.

50 + 10e/a = 40 + 40e/3a

So, e/a = 3

So total length is 50 + 10e/a = 80.

Hence, option (a).

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