A frog tries to come out of a dried well 4.5 m deep with slippery walls. Every time the frog jumps 30 cm, slides down 15 cm. what is the number of jumps required for the frog to come out of the well?

Total distance to be jumped by frog to come out = 4.5 m = 450 cm.

Frog jumps 30 cm and slips 15 cm, which means that, in a jump he ascends 30 – 15 = 15 cm.

In 28 such jumps he will ascend to 28 × 15 = 420 cm.

Now only 30 cm remain to come out, which the frog will jump in the next (29th) jump.

In the last jump frog will not slip because he will be outside the well