Can you start the fire using two pieces of wood?

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?

Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

Take away my first letter, then take away my second letter. Then take away the rest of my letters, yet I remain the same. What am I?

Find The Next Number in this series.
1, 2, 6, 42, 1806 ?

I am thinking of a five-digit number such that:
The first and last digits are the same, their submission is an even number and multiplication is an odd number and is equal to the fourth number. Subtract five from it and we obtain the second number. Then divide into exact halves and we get the 3rd number.

What number I am thinking of?

Solve the alphametic puzzle by replacing the alphabet with the number.

S T O R M +
S O L E S
=========
T O W E L
=========

What can go up a chimney down, but can’t go down a chimney up?

What will you call your mother's brother's brother-in-law?

10+10 and 11+11 can give you the same answer.

Explain how?