Cogito
Grade 5 Math · Chapter 6 · Lesson 4
Multiplying Mixed Numbers
Turn them into pieces first.
10 problems · about 16 minutes · 5.NF.B.6
What this lesson teaches
The child multiplies mixed numbers and solves real-world problems with them.
- Turn mixed numbers into improper fractions first.
- Then multiply the tops and the bottoms as usual.
- A mixed number is over 1, so the answer grows.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Area with Fractional Sides: 1/2 by 2/5. What is the bottom number of the area?
Answer 10
Why 2/10, which is 1/5.
Review — Multiplying as Scaling: What is 3/5 × 25?
Answer 15
Why 15.
Warm Up
Straightforward practice. Get the method working first.
4 problems1 1/2 × 6. What is the answer?
Answer 9
Why 9.
What is the first step when multiplying mixed numbers?
Answer Turn them into improper fractions.
Why Convert first, then multiply the tops and bottoms.
2 1/3 in thirds. What is the top number?
Answer 7
Why 2 × 3, plus 1.
1 1/2 × 4. What is the answer?
Answer 6
Why 3/2 × 4 = 12/2.
Build It Up
The same ideas with more to keep track of.
2 problems2 1/2 × 2. What is the answer?
Answer 5
Why 5/2 × 2 = 10/2.
Is 2 1/4 × 6 bigger or smaller than 6?
Answer Bigger.
Why 2 1/4 is more than 1.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Recipe: 1 1/2 cups, doubled. How many halves in all?
Answer 6 halves
Why 6/2, which is 3 cups.
The Planks: 4 planks of 2 1/4 metres. How many quarters in all?
Answer 36 quarters
Why 36/4, which is 9 metres.