A person has to touch the top of a tower of 60 feet height. In every second, he climbs 5 feet, but slips down 4 feet. In how many seconds would he touch the top ?

The correct answer is (A) 56.

Step-by-step mathematical working:

• Total height of the tower = 60 feet.
• In each second, net climb = $5 - 4 = 1$ foot.
• On the final second, when the person climbs 5 feet and reaches/touches the 60-foot top, he does not slip back down.
• Height to cover at the net rate of 1 ft/sec = $60 - 5 = 55$ feet $⟹55$$\implies$ 55 seconds.
• In the 56th second, he climbs 5 feet from 55 feet: $55 + 5 = 60$ feet (touches the top).
• Total time taken = 56 seconds.