Question: Find the answer to the math problem: Rory makes a cake that weighs 20 ounces. She cuts into 8 pieces. Rory and her mom each have a piece. How much does the remaining cake weigh?
Answer: 
Each piece of Rory’s cake weighs 20 ounces / 8 pieces = 2.5 ounces.
If Rory and her mom each have a slice, they will have eaten 2.5 ounces + 2.5 ounces = 5 ounces.
The rest of the cake weighs 20 ounces – 5 ounces = 15 ounces.