What is the final concentration if 50.0 ml of a 2.00 m solution are diluted to 500.0 ml? ?

In order to calculate the final concentration of a dilution, it is important to memorise and remember the following equation:

C1V1/C2V2
Where: 
C1 = Initial concentration
V1 = Initial volume
C2 = Final concentration
V2 = Final volume

We are given three of the four, and we are asked to calculate the final concentration in moles, so we may substitute these given values into our equation as follows:

C1V1 = C2V2
(2.00m)(50.0 mL) = (C2)(500mL)
100 = C2(500mL)
C2 = 0.2 m

In the final step, we simply divide 100 by 500 to get our final concentration value.