Charles and Lisa were having a watermelon eating contest. They ate twelve slices of watermelon between the two of them. Lisa ate two times as many slices of watermelon than Charles. How many slices of watermelon did Lisa eat?

8 slices

Step-by-step explanation:

Let the watermelon eaten by Charles be A and Lisa be B

They ate 12 slices of watermelon between them

That's

A + B = 12

Also, Lisa ate 2 times as Charles

that's

B = 2A

We no have two equations

1. A + B = 12

2. B = 2A

Substitute 2A for B into the first equation

A + B = 12

A + 2A = 12

3A = 12

Divide both sides by 3

3A/3 = 12/3

A = 4

Charles ate 4

Recall Lisa B ate twice as Charles A

B = 2A

B = 2 x 4

B = 8

Lisa ate 8 slices of watermelon