What does this mathematical rebus means ?

A man who was outside in the rain without an umbrella or hat didn’t get a single hair on his head wet. Why?

What will be the best approach to finding all the prime numbers less than 75 that leave an odd reminder when we divide them with 5?

What does the following represent?

N N N N N N N

A A A A A A A

C C C C C C C

I am five letter word that is under you.
If you remove my 1st letter, then I am over you.
If you remove my 1st and 2nd letters then I am all around you.

Who am I?

Which digit occurred maximum times between the number 1 and 1000?

What number do you get when you multiply all of the numbers on a telephone's number pad?

A man stands on one side of a river, his dog on the other. The man calls his dog, who immediately crosses the river without getting wet and without using a bridge or a boat. How did the dog do it?

Find the next number in the series below

21 32 54 87 131 ?

What can run but never walk, have a mouth that never speaks, have a head that never weeps, and have a bed but never sleeps?