Which number should replace the question mark?

A mother is 21 years older than her child. In exactly 6 years from now, the mother will be exactly 5 times as old as the child.
Where's the father?

How can you tell a raw egg from a hard-boiled egg?

What number divided by 4 is the same as that number minus 4?

Christina is practising her dance steps along with her friends. In a particular sequence, all of them form a row. At that point, Niharika is standing in the 4th position from either end of the row.
Can you find out how many girls are practising together?

What goes up but never comes down?

I’m orange, I wear a green hat and I sound like a parrot. What am I?

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

A professor thinks of two consecutive numbers between 1 and 10.
'A' knows the 1st number and 'B' knows the second number

A: I do not know your number.
B: Nor do I know your number.
A: Now I know.

What are the four solutions for this?

By what process could you make a 'Tea-Table' into food?