A ladder has 10 steps.A labourer has to carry some weight to the top. He climbs the ladder 2 steps up in one second and 1 step down in the next second by dancing on a famous tune. In how many seconds he would reach the top.

**ANSWER:** labour goes in 1 sec = 2 steps

then,

he get down in next 2 sec = 1 step .

so, finally he goes up in 1 step in = 3sec .

hence , he goes 10 steps in =

3×10 = 30 sec .