Cogito
Grade 6 Math · Chapter 3 · Lesson 2
Multiplying and Dividing Decimals
Count the places, and check the size.
10 problems · about 17 minutes · 6.NS.B.3
What this lesson teaches
The child multiplies and divides multi-digit decimals fluently and checks answers by estimating.
- Multiply as whole numbers, then count the decimal places.
- To divide by a decimal, scale both until the divisor is whole.
- Check the size of the answer against the factors.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Dividing a Fraction by a Fraction: 3/4 ÷ 1/12 = ?
Answer 9
Why 9.
Review — Converting Units with Rates: 5 km in metres?
Answer 5000
Why 5000 m.
Warm Up
Straightforward practice. Get the method working first.
4 problems9 ÷ 0.3 = ?
Answer 30
Why 30.
Will 0.4 × 0.5 be bigger or smaller than 0.4?
Answer Smaller.
Why A factor under 1 shrinks it.
0.2 × 0.3, in hundredths?
Answer 6
Why 2 × 3, two places.
8 ÷ 0.4 = ?
Answer 20
Why 80 ÷ 4.
Build It Up
The same ideas with more to keep track of.
2 problems1.2 ÷ 0.3 = ?
Answer 4
Why 12 ÷ 3.
0.5 × 0.8, in hundredths?
Answer 40
Why 5 × 8, two places.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Fabric: 4.5 metres cut into 0.5 metre pieces. How many pieces?
Answer 9 pieces
Why 9 pieces.
The Cost: 0.4 × 0.6, in hundredths?
Answer 24 hundredths
Why 0.24.