Why is the Hole below a Lock?

When my father was 31 I was 8. Now he is twice as old as me. How old am I?

There is a shop where written:
Buy 1 for $1
10 for $2
100 for $3
I needed 999 and still only paid $3. How could this be financially viable for the shop-keeper?

What country can make you shiver?

A thief enters a store and threatens the clerk, forcing her to open the safe. The clerk says, “The code for the safe is different every day, and if you hurt me you’ll never get the code.” But the thief manages to guess the code on his own. How did he do it?

What number comes next in this sequence:
7 8 5 5 3 4 4 _

What can you deduce from the following BrainBat?

CRY
LMKI

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?

What goes up but never comes down?

What is the next number in the series?

15 29 56 108 208 ?