How it works
Say about how much first. Then cut to one bottom, or multiply across, and check the size.
To add fractions with different bottoms, cut them to the same bottom.
An estimate tells you if your answer is sensible.
Worked examples
Add
- Mia pours 1/8 of a cup of flour and then 3/4 of a cup.
- 3/4 is 6/8, so 1/8 + 6/8 = 7/8.
- She has 7/8 of a cup, a bit less than a cup.
Take away
- Leo has 5/6 of a liter and drinks 1/12 of a liter.
- 5/6 is 10/12, so 10/12 − 1/12 = 9/12.
- 9/12 is 3/4 of a liter.
Estimate
- Ava cuts 1/12 of a meter and 1/4 of a meter.
- 1/12 is small and 1/4 is a quarter.
- About 1/2 of a meter at most: it's about a third.
A taste of the worksheet
These are the first problems of set A. The printable sheet has many more, with an answer key.
- Mia puts 11/12 cup of flour in a bowl. Then she adds 1/2 cup more. About how much flour is in the bowl?
- Mia has 3/4 cup of flour. She uses 3/8 cup to bake bread. How much flour is left? ___ cup
- Mia measures 1/2 cup of flour, then 11/12 cup more. How much flour does she have in all?
- 1/3 + 1/4 = 2/7
- 5/6 − 1/3 = 1/2
Words to know
- common bottom
- A bottom number both fractions can share.
- estimate
- A close answer.
Watch out for
- Cut to the same bottom before adding.
- Estimate first.
- Simplify at the end.
Try it
1/2 + 1/4 = ?
3/4. 1/2 is 2/4.
2/3 − 1/6 = ?
1/2. 2/3 is 4/6.
Is 1/3 + 1/4 more or less than 1/2?
more. 7/12 is more than 6/12.
What do you do before adding fractions with different bottoms?
cut them to the same bottom. Match.
For grown-ups
Cook with fractions of a cup and talk through the adding.