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

Solve below rebus puzzle?

Once while in his court, King Akbar asked Birbal to write something on a wall that makes one sad when read in good times and makes one happy when read in sad times.

He took only a few moment and wrote something that fit the requirements. What did he write?

Can you fill the blank with the correct number?

6 30 870 756030 _____

I cannot talk, but I always reply when spoken to. What am I?

One night, a woman receives a call from the police. They tell her that her husband was murdered and that she should come to the crime scene as soon as possible. The woman drops the phone, shocked, and drives 20 minutes to the crime scene. As soon as she reaches the crime scene, the police arrest her and she is convicted of murder. How do the police know she committed the crime?

I am white when I am dirty, and black when I am clean. What am I?

What's a single-digit number with no value?

I have teeth but i don't bite. Who Am I ?

Until it is measured, not known. Yet how you miss it when it has gone. What is it?