Cogito
Grade 5 Math · Chapter 4 · Lesson 1
Multiplying by Powers of Ten
Every digit shifts one place.
10 problems · about 15 minutes · 5.NBT.A.2, 5.NBT.B.7
What this lesson teaches
The child multiplies and divides decimals by powers of ten and explains the shift.
- Multiplying by 10 shifts every digit one place left.
- Dividing by 10 shifts every digit one place right.
- "Add a zero" is not a rule that works on decimals.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Estimating with Decimals: Estimate 7.8 + 2.1 to the nearest whole numbers.
Answer 10
Why About 10.
Review — Subtracting Decimals: 1 − 0.28, in hundredths?
Answer 72
Why 72 hundredths, which is 0.72.
Warm Up
Straightforward practice. Get the method working first.
4 problems0.08 × 100 = ?
Answer 8
Why 8.
What happens when you multiply by 10?
Answer Every digit moves one place left.
Why The digits shift. "Add a zero" fails on decimals.
0.5 × 10 = ?
Answer 5
Why 5 tenths becomes 5 wholes.
0.06 × 100 = ?
Answer 6
Why Two places left.
Build It Up
The same ideas with more to keep track of.
2 problems70 ÷ 100, in hundredths?
Answer 70
Why 0.7 is 70 hundredths.
4.2 × 100 = ?
Answer 420
Why Two places left.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsTen Times: 2.6 × 10, in tenths?
Answer 260 tenths
Why 26, which is 260 tenths.
A Tenth of It: 84 ÷ 10, in tenths?
Answer 84 tenths
Why 8.4, which is 84 tenths.