You have 100 killograms of puzzling mangoes, which are 99 percent water by weight.

You let them dehydrate until they are 98 percent water.

How much do they weigh now ?

Perhaps surprisingly, the mangoes now weigh 50 kilograms. The sack of mangoes originally weighed 100 kilograms, and 1 percent of its weight, or 1 pound, was non-water. If that 1 pound now makes up 2 percent of the total weight, then the total weight must be 50 kilograms.