Question

Ed had 1.2 liters of water. He drank 200 milliliters. How much does he have left?

Answer 1

1.2 liters=1200 mililiters (ml) => he has 1200-200=1000 ml=1 liter left

Answer 2

1 milliliter is .001 of a liter, so 200 milliliters is .2 of a liter.  Thus, taking away .2 of a liter from 1.2 liters leaves 1 liter.