Question

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 $60$ stairs$?$

Answer 1

Finding the number of seconds to climb $\mathbf{60}$stairs.

Given, Number of steps climbed by Reena every second $=5$ stairs

Number of steps climbed down by Reena the next second $=2$ stairs

For every $2$ second, the number of steps climbed by Reena $=3$stairs

So, Reena will climb $1$ stairs in $\frac{2}{3}$ seconds.

Total number of steps climbed by Reena $=60$ stairs

Therefore, the time taken by Reena to climb $60$ stairs $=\frac{2}{3}\times 60$ $=40\mathrm{seconds}$

Time taken by Reena to climb $60$ stairs $=40–1=\mathbf{}\mathbf{39}\mathbf{}\mathit{s}\mathit{e}\mathit{c}\mathit{o}\mathit{n}\mathit{d}\mathit{s}$

This is because when she climbs $5$ stairs, she reaches 60 stairs which makes her not to climb down the next second.

Therefore, the time taken by Reena to climb $\mathbf{60}\mathbf{}\mathbf{stairs}\mathbf{}\mathbf{is}\mathbf{}\mathbf{39}\mathbf{}\mathbf{seconds}\mathbf{.}$