There are are five things wrong with this sentence; only geniuses will be able to to spot all of the mitstakes

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?

Why is the Hole below a Lock?

I am a number I am not an odd number I am higher than 90 I am not higher than 100 If you subtract me from 100, you get nothing. What number am I?

You walk into a room that contains a match, a kerosene lamp, a candle and a fireplace. What would you light first?

When Jack was six years old he hammered a nail into his favourite tree to mark his height. Ten years later at age sixteen, Jack returned to see how much higher the nail was. If the tree grew by five centimetres each year, how much higher would the nail be?

No matter how little or how much you use me, you change me every month. What am I?

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

John is a strange liar.

He lies on six days of the week, but on the seventh day, he always tells the truth.

He made the following statements on three successive days:

Day 1: "I lie on Monday and Tuesday."
Day 2: "Today, it"s Thursday, Saturday, or Sunday."
Day 3: "I lie on Wednesday and Friday."

On which day does John tell the truth?

How many triangles can you count in the figure given?