operations · Year 4 · AC9M4N05
Multiply by multiples of 10 and 100
Split each multiple of ten into a basic fact and a power of ten: 30 × 40 is 3 × 4 = 12, and there are two zeros, so 1200. Keep any zero the basic fact makes: 50 × 60 is 5 × 6 = 30 with two more zeros, so 3000. To find a missing factor, take the same number of zeros off both numbers and divide.
Sample questions
50 × 2 = ?
- Basic fact: 5 × 2 = 10.
- 50 and 2 have 1 zero altogether, so the answer is 10 with 1 zero on the end.
- 50 × 2 = 100.
Answer: 100
3 × 70 = ?
- Basic fact: 3 × 7 = 21.
- 3 and 70 have 1 zero altogether, so the answer is 21 with 1 zero on the end.
- 3 × 70 = 210.
Answer: 210
4 × 40 = ?
- Basic fact: 4 × 4 = 16.
- 4 and 40 have 1 zero altogether, so the answer is 16 with 1 zero on the end.
- 4 × 40 = 160.
Answer: 160