A Monkey climbs a 12 meters high slippery pillar. In his first minute, he climbs 2 meters and in the next minute, he slips one meter down. In this way, how much time will he take to reach the top of the pillar?

The trick is that the monkey can only slip after a climb, so once he reaches the top on a climb, he stays there. Work in two-minute cycles: each cycle he climbs 2 m and slips 1 m, a net gain of 1 m.

After 20 minutes (10 cycles) he is at 10 m. In the 21st minute he climbs 2 m and reaches 12 m. He never slips back from the top, so the answer is 21 minutes.

• A) 10 minutes: Wrong. After 10 minutes (5 cycles) he is only at 5 m.
• C) 12 minutes: Wrong. This assumes a net gain of 1 m per minute. After 12 minutes he is at 6 m.
• D) 11 minutes: Wrong. After 10 minutes he is at 5 m, and in minute 11 he reaches only 7 m.

Core concept: net progress in cyclic climb-and-slip problems, with the final climb treated separately. This is the same logic used in time-and-work and sequence questions, where you model the repeating cycle and then handle the last step on its own.

Trap: Aspirants divide the height by the net daily or minute gain (12 divided by 1) and forget that the final climb needs no slip. Always check where the cycle stops.