Subject: Weight problem

Name: Lori Speir
Who is asking: Parent
Level: All

Question:
If I have a 100 pound watermelon and it is 99% water. If it sits out in the sun all day and is now only 98% water what does it weigh now?

Rather than thinking about the part of the watermelon that is water, think in terms of the part that is not water. This part does not change as the watermelon sits in the sun.

At the start 1% of the 100 pound watermelon is not water, that is 1 pound of the watermelon is not water. After sitting in the sun this 1 pound of material is 2% of the watermelon since the part that is water is 98%. The problem can thus be reworded to ask, what weight is a watermelon if 2% if it weighs 1 pound?

Suppose the watermelon weighs W pounds then 2% of W is 1, or W(2/100) = 1 so W is 50 pounds.