Question

Reena climbs up 5 stairs every second and then climb down 2 stairs over the next second how many second will it take to climb 60 stairs

Answer 1

If Reena climbs up 5 stairs every second and then climbs down 2 stairs over the next second, how many seconds will she take to climb up 60 stairs?
It's taking 2 seconds for climbing 3 stairs.

So if you go without thinking then laymen would say it would take 20*2=40seconds

But it's not the case.

For 17 times ,a person will climb 17*3=51stairs

For 18 times , person will climb 54stairs

For 19 times ,person climbs 57 stairs

For 20 times , person takes 60 stairs

Till 19 times, it took 19*2=38 seconds

For 20 times, 38+(3/5)=38+0.6=38.6seconds

The answer is 38.6 seconds.

Answer 2

She will take 39 seconds to climb 60 stairs.
Explanation:
Reena climbs up 5 stairs every second
She climb down 2 stairs over the next second
The net climb for Reena is 3 stairs per 2 seconds.
Total she has to climb is 60 stairs
So she should take (60/3) *2=40 seconds.
Since in the last second she will not fall, she will reach a second before, that is by 39th second.