5- HOW TO CALCULATE DILUTIONS:
We have a solution already made: it is called the stock solution.
We want to use it to make another solution of the same type but more diluted.
The question is
how much should I dilute the stock solution to make it.
The magic formula to figure it out is the following:
vol new x conc new = vol st x conc st
Vol new : volume of the new solution
conc new : concentration of the new solution
vol st : volume of the stock solution that will be part of the new solution
conc st : concentration of the stock solution
Go through the two examples of dilutions and then try to do the exercises by yourself.
Example #1 
Example #2
Exercise #1
Exercise #2