Subtracting Fractions With borrowing

Just like in whole number subtraction, sometimes you need to borrow when subtracting fractions.

Example 1: Whole number – mixed number If you order 5 pizzas and your family eats 3 and 2/5 of them, how much pizza is left?

Always write the equation vertically:

Start with 5 pizzas:

Uh, oh! I can’t take 2/5 of a pizza from nothing!

That’s OK! Take one pizza and turn it from a whole pizza into one with five slices! Now you have four whole pizzas and one whole pizza split into five slices!

Now just subtract!

Answer: We have 1 and 3/5 of a pizza left.

Example 2: Mixed number – Mixed number Maria’s family had a party and her mom made lasagnas. At the end of the night there were 4 and 5/8 pans of lasagna left. Maria’s mom packed up 2 and ¾ pans for her grandparents and cousins to take home. How much did they have left to eat for leftovers the next day?

Start with 4 and 5/8 pans of lasagna.

Uh, oh! I can’t subtract fractions with unlike denominators!

First, convert the fractions to have the same denominator. In this case, the least common denominator is 8.

Uh, oh! I can’t take 6/8 away from 5/8!

Now, you need to borrow a whole from the four and make it into eighths. You already have 5/8, so adding 8/8 will give you 13/8. 1 2 9 10 3 4 11 12 5 6 13 7 8

Set up your equation and subtract!

Answer: Maria will have 1 and 7/8 of a pan of lasagna left for leftover night.

Now you try!