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?

You are presented with three boxes. One of them has a red ball inside and the other two have a black ball inside each of them. You are asked to pick up the one with red ball and you pick one. Now, one of the other boxes is opened and it is found to have a black ball.

You are presented with a chance to change your box with the one that is left closed. Will you change your box? Why or why not?

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

Solve the rebus riddle in the picture below.

Decode below rebus
D
N
A
T
S , D

The day after tomorrow will be three days before Tuesday. Can you find out what is today?

He digs out tiny caves and stores gold and silver in them. He also built bridges of silver and made crowns of gold. They are the smallest you could imagine. Sooner or later everybody needs his help, yet many people are afraid to let him help them. Who is he?

If you toss a coin 10 times and it lands heads up every time, what are the chances it will land heads up if you toss it again?

A bridge is about to collapse. There are four people P, Q, R and S on one of the sides. Before the bridge collapses, they want to cross it. Now since the bridge is too weak, it can only stand the weight of two people at a time. Also, it is night time and nothing is visible. They have just one torch with them.

Now P takes one minute to cross the bridge, Q takes two minutes to cross, R takes five minutes to cross and S takes ten minutes to cross.

The bridge will collapse in seventeen minutes. How will they be able to cross the bridge before it collapses?

It's a protector.
It sits on a bridge.
One individual can see directly through it, while others wonder what it hides.

What is it?