Cogito
Grade 5 Math · Chapter 5 · Lesson 2
Adding Unlike Fractions
Match, then count.
10 problems · about 15 minutes · 5.NF.A.1
What this lesson teaches
The child adds and subtracts fractions with unlike denominators.
- Rewrite both fractions in one shared unit.
- Then count the units.
- Never add the bottom numbers.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Finding a Common Denominator: 2/3 written in fifteenths. What is the top number?
Answer 10
Why 10/15.
Review — Dividing Decimals: How many halves fit into 9?
Answer 18
Why 18 halves.
Warm Up
Straightforward practice. Get the method working first.
4 problems2/3 + 1/4, in twelfths. What is the top number?
Answer 11
Why 11/12.
What are the two steps for adding unlike fractions?
Answer Match the units, then count them.
Why Match first, then count. Never add the denominators.
1/2 + 1/3, in sixths. What is the top number?
Answer 5
Why 3/6 + 2/6.
1/4 + 2/5, in twentieths. What is the top number?
Answer 13
Why 5/20 + 8/20.
Build It Up
The same ideas with more to keep track of.
2 problems3/4 − 1/6, in twelfths. What is the top number?
Answer 7
Why 9/12 − 2/12.
5/6 − 1/2, in sixths. What is the top number?
Answer 2
Why 5/6 − 3/6.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Two Jugs: 1/2 litre plus 1/4 litre, in quarters. What is the top number?
Answer 3
Why 3/4 of a litre.
The Walk: 2/3 mile plus 1/6 mile, in sixths. What is the top number?
Answer 5
Why 5/6 of a mile.