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

Count the number of balls in picture below:

There are three Athletes (John, Tarun and Harish) and their individual Coaches (Jacob, Meenaxi and Priyanka) standing on the shore.
No Coach trusts their Athlete to be near any other Coach unless they are also with them.
There is a boat that can hold a maximum of two persons.
How can the six people get across the river?

One absent-minded ancient philosopher forgot to wind up his only clock in the house. He had no radio, TV, telephone, internet, or any other means for telling time. So he travelled on foot to his friend's place a few miles down the straight desert road. He stayed at his friend's house for the night and when he came back home, he knew how to set his clock. How did he know?

What famous saying does this rebus mean?

COME SERVED <---
COME SERVED
COME SERVED
COME SERVED
COME SERVED

If you had a pizza with crust thickness 'a' and radius 'z', what's the volume of the pizza?

I came first on earth but second on the heaven.
I also came twice in a week but found just once in a year.
I stay away from months but you can find me in February.

What am I?

What kind of band never plays music?

Can you make numbers like 24, using numbers 3,3,7 & 7 with any arithmetic operator?

When a clock is observed, the hour hand is at a minute mark and the minutes hand is six minutes ahead of it.

When the clock is observed again after some time, the hour hand is precisely on a different minute mark and the minute hand is seven minutes ahead of it.

Can you calculate how much time has elapsed between the two observations?