Together, Amy and Betty have 20 apples. Amy has three times the number of apples that Betty has. How many more apples than Betty does Amy have?
I need to find the difference between the number of apples that Amy and Betty have. I can use algebra to represent the situation with variables and equations. Let x be the number of apples that Betty has, and let y be the number of apples that Amy has. Then I have two equations: x + y = 20 and y = 3x. I can substitute y = 3x into the first equation and get x + 3x = 20. Simplifying, I get 4x = 20, so x = 5. This means that Betty has 5 apples and Amy has 3 times as many, so y = 3x = 15. To find the difference, I subtract the smaller number from the larger number: y - x = 15 - 5 = 10. So Amy has 10 more apples than Betty. 