Which number should replace the question mark?

Teacher ask the student

'Why are you standing on that chair in music class ?'.

what did student replied ?

You are in a room that has three switches and a closed door. The switches control three light bulbs on the other side of the door. Once you open the door, you may never touch the switches again. How can you definitively tell which switch is connected to each of the light bulbs?

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

How can you drop a raw egg from a height onto a concrete floor without cracking it?

Replace the question mark in the picture below.

You see a boat filled with people, yet there isn’t a single person on board. How is that possible?

A bus driver was heading down a street in Mexico. He went right past a stop sign without stopping, he turned left where there was a "no left turn" sign, and he went the wrong way on a one-way street. Then he went on the left side of the road past a cop car. Still - he didn't break any traffic laws. Why not?

Five lovely ladies(Sophia, Isabella, Madison, Emma and Olivia) planned a picnic.

They each buy one thing each for the picnic.

Sophia, Emma and Olivia got a drink : orange-Juice, apple-juice, and mango-juice.
Olivia got the drink with the same letter as the one in her first name.
Emma loves mango-juice.
The other two bring some food : chocolates and pizza.
Also Madison is allergic to cheese.

So which ladies bought what ?

How will you measure 15 minutes using two hourglasses of 7 minutes and 11 minutes respectively?