What is the fewest number of coins that would be required in order to make sure each and every coin touches exactly three other coins?

There’s a one-story house in which everything is yellow. Yellow walls, yellow doors, yellow furniture. What colour are the stairs?

Can you count the number of quadrilaterals in the picture below?

Which city is three-fifths chick two third cat and 50% goat?

John went to meet his friend Jacob, but when he was about to reach the main gate, John notices that Jacob had a mighty dog who was fastened to the tree. The chain is long enough that it allows the dog to reach the main gate.

How can the John reach the main gate?

Until it is measured, not known. Yet how you miss it when it has gone. What is it?

What does a man do only once in his lifetime, but women do once a year after they are 29?

You can hear me, but you can't touch or see me.

What am I?

When 99 is considered higher than 100?

The host of a game show offers the guest a choice of three doors. Behind one is an expensive car, but behind the other two are goats.
After you have chosen one door, he reveals one of the other two doors behind which is a goat (he wouldn't reveal a car).

Now he gives you the chance to switch to the other unrevealed door or stay at your initial choice. You will then get what is behind that door.

You cannot hear the goats from behind the doors, or in any way know which door has the prize.

Should you stay, or switch, or doesn't it matter?