PEAZIT Aha card
Go straight to resources ↓Why does the decimal point move in multiplication?
A tenth times a tenth is a hundredth. You can multiply without decimal points, but then undo both changes of scale.
| Value | Meaning | Fraction |
|---|---|---|
| 1.2 | 12 tenths | 12/10 |
| 0.3 | 3 tenths | 3/10 |
| product | 36 hundredths | 0.36 |
One worked example
- 12 × 3 = 36First multiply the whole numbers.
- (12/10) × (3/10) = 36/100Both factors were enlarged tenfold, so the product was enlarged a hundredfold.
- 1.2 × 0.3 = 0.36Restore the correct size: 36 ÷ 100.
Watch out: Multiplication does not always make a number larger. A positive factor below one selects a part of the amount.
Goal, prerequisites and card origin
What you will learn: Multiply decimals and check the size of the answer.
What you need first: Multiplication facts; tenths and hundredths.
An original PEAZIT working card. Independent expert review and effectiveness testing have not yet taken place. · v1
Show connections
A tenth times a tenth is a hundredth. You can multiply without decimal points, but then undo both changes of scale.