Subtraction in the Real World
Activity: Making Change
Suppose you have $25.90 in cash (two $10 bills, five $1 bills, and nine dimes) and you owe a friend $16.87. How will you break the $25.90 in order to pay off your debt?
Start with the $16.87. You can give your friend a $10 bill. What will you still owe her?
After giving your friend $10, you will still owe her . You still have five $1 bills, so you fork those over, too! Now you only owe her .
Since your friend won’t budge, you need to make change for your remaining $10 bill. Let’s say you break it into a $5 bill and five $1 bills. Then you hand over $1 to your friend.
At this point, your debt is now . After giving your friend eight dimes, the amount you still owe is .
Taking your last dime and trading it for a nickel and five pennies, you hand over the last 7 cents you owe. Now you’ve erased your debt!