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 seconds, the number of steps climbed by Reena = 3 stairs
Total number of steps climbed by Reena = 60 stairs
Therefore, time take by Reena = (60/3)(20) = 40 seconds
Time taken by Reena to climb 60 stairs = 40 – 1 = 39 seconds
This is because when she climbs 5 stairs, she reaches 60 stairs which makes her not to climb down the next second.