Calculate how much glycerol you would need to make 200 ml of a 20% (v/v) glycerol solution. (Glycerol is a liquid and the initial concentration is 100%).

The key to solving this problem is to found how much the weight of glycerol needed to make the solution. The calculation would be:

weight = volume * concentration

weight1 = weight2

volume1 * concentration1 = volume2 * concentration2

200ml * 20% = volume2 * 100%

volume2 = 200ml * 20/100

volume2 = 40ml