You wish to count the number of bacteria in 1 ml of a solution but there are too many to count! So you mix the 1 ml with 9 ml of water to dilute it, and then draw 1 ml of the new mixture. Still too many, so you mix with 9 ml of water and draw 1 ml of new solution and now count 75 nasty little bacteria swimming around. How many bacteria in the original solution?