A squirrel starts climbing up a tree at the speed of 6 metres a minute but after every 6 metres it slips down 4 metres in the next minute. It will be able to reach the top 120 metres high in
(a)20 minutes
(b)60 minutes
(c)115 minutes
(d)$1 \frac{1}{2}$ hours
Answer
Answer (as printed): C
Explanation
In 2 min, the squirrel climbs $(6-4) \mathrm{m}=2 \mathrm{m}$. In (2 × 57), i.e., 114 min, the squirrel climbs $(2 \times 57) \mathrm{m}$ $=114 \mathrm{m}$. In 115 min, the squirrel climbs $(114+6) \mathrm{m}=120 \mathrm{m}$ to reach the top.