It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

A famous swimmer can swim downstream in a lake in exactly 40 minutes with the lake current.
He can swim upstream in that lake in exactly 60 minutes against the lake current.
The length of the lake is 2 km.

How long he can cover the distance of one side at a still lake with no current?

John was a very careless driver, so his owner Jacob gave him an offer that he will get an incentive of Rs.30 for every bottle box he delivered without breaking it and he will be charged Rs.90 for every bottle box he broke. Jacob gave John 100 bottles-box to deliver. After delivery, Jacob paid John Rs.2400. How many bottles-box did John break?

What has many keys but can’t open a single lock?

Find the next number in the series.
1 10 24 43 67 ?

What does this mathematical rebus means ?

Can you guess the name of the month by looking the below rebus ?

Give it food and it will live; give it water and it will die.

What has six faces, but does not wear makeup, has twenty-one eyes, but cannot see?

Place the numbers from 1 to 9 in the circles in a manner that each side of the triangle sums up to 17.