Which number should replace the question mark?

I get hot but I never sweat,
I cook food but I am not a chef,
I have a door but you can't enter me,
I have a light but I am not a lamp.
Who am I?

The person who makes it has no need for it; the person who buys it has no use for it. The person who uses it can neither see nor feel it. What is it?

If 5 cats catch 5 mice in 5 minutes, how long will it take one cat to catch a mouse?

Can you find out which number multiplied by itself will give the output as 12345678987654321?

Before Mount Everest was discovered, what was the highest mountain in the world?

A worker is to perform work for you for seven straight days. In return for his work, you will pay him 1/7th of a bar of gold per day. The worker requires a daily payment of 1/7th of the bar of gold. What and where are the fewest number of cuts to the bar of gold that will allow you to pay him 1/7th each day?

Replace the question mark in the picture below.

In a stable, there are men and horses. In all, there are 22 heads and 72 feet. How many men and how many horses are in the stable

Why Aeroplane windows are round?