A monkey ascends a greased pole 12 metres high. He ascends 2 metres in first minute and slips down 1 metre in the alternate minute. In which minute, he reaches the top ?
Select
A) 21 st B) 22 nd C) 23 rd D) 24 th E) none of these

Rationale: in 2 minutes , he ascends = 1 metre ∴ 10 metres , he ascends in 20 minutes . ∴ he reaches the top in 21 st minute . answer b
Answer: B