Puzzle No. 2 & 3

Well, many days have passed since I published the last puzzle. The solution is simple: 2 hits of 11 metres each one. Dany was the one who solve it. The solution he posted is on the comments of the previous post. Look it and check out your own answer.

This time we have two. They are short and easily to solve, just read with attention the problem.

First One

There is a kind of mouse that can have 12 little mice in one month. This little mice, when they are 2 months old, can have another little mice.
If you buy a female mouse of this kind. How many mice you have after 10 months?

Second One

Imagine a big barrel plenty of various things. It is too heavy due to the objects inside it. But there is a thing that you can put in the barrel and decrease its weight. What is it?

A clue:

It doesn't take up any space on the barrel but you can see it.

Remember don't look for the answers and if you have any doubt ask me. See you!!