Week 07 · Unlike denominators
Tuesday
Add unlike fractions
// Add and subtract fractions with different denominators
⏱ about 15 min
Tuesday: Add unlike fractions
Riley is painting a sign for the trail. In the morning he paints 1/2 of it.
In the afternoon he paints 1/3 more.
"I added the tops and the bottoms," Riley says. "I painted 2/5 of the sign."
Bennie looks at the sign and rubs his chin.
"But 2/5 is less than 1/2, and you painted more than half in the morning alone," he says.
Riley laughs. "You are right! Let me use sixths, like yesterday."
Learn it: same-size parts first
We can only add parts that are the same size.
Rewrite 1/2 as 3/6 and 1/3 as 2/6.
Now add the sixths: 3/6 + 2/6 = 5/6.
Riley painted 5/6 of the sign.
Sums can be greater than 1.
2/3 + 5/4 = 8/12 + 15/12 = 23/12. That is 1 11/12.
ONE STEP AT A TIME
- Read the question.
- Tap your answer.
1/2 + 1/3 = 3/6 + ?/6
1/4 + 2/3 = ?/12 + 8/12
2/5 + 1/2 = 4/10 + ?/10
3/4 + 1/6 = ?/12 + 2/12
ADD THE FRACTIONS
- Read the question.
- Tap your answer.
1/2 + 1/3 = ?
1/4 + 2/3 = ?
2/5 + 1/2 = ?
1/6 + 1/4 = ?
SUMS GREATER THAN 1
- Read the question.
- Tap your answer.
3/4 + 2/3 = ?
2/3 + 5/4 = ?
5/6 + 1/2 = ?
7/8 + 3/4 = ?
ADD 2/3 + 1/4
- Think about how Riley adds.
- Tap the steps in order.
1First
2Next
3Last
Make the denominators the same. Then add only the numerators.
| Sentence | True or false? |
|---|---|
| 1/2 + 1/3 = 2/5 | ? |
| 1/2 + 1/4 = 3/4 | ? |
| 2/3 + 1/6 = 5/6 | ? |
| 1/3 + 1/3 = 2/6 | ? |
WHY THIS EXERCISE1/2 + 1/3 is 5/6, and 1/3 + 1/3 is 2/3.
Try it
Find measuring cups for 1/2 cup and 1/4 cup, and a bowl.
Pour 1/2 cup of water into the bowl, then 1/4 cup more.
How many 1/4 cups of water are in the bowl? What fraction of a cup is that?
Pour 1/2 cup of water into the bowl, then 1/4 cup more.
How many 1/4 cups of water are in the bowl? What fraction of a cup is that?
Draw fraction strips to show 1/2 + 1/3 = 5/6.
Well added! Tomorrow we subtract fractions and use mixed numbers.