Grades 2–3
A Doubling Strategy for 2s, 4s, and 8s
×2 is one double. ×4 doubles again. ×8 doubles a third time.
Multiplying by 2 is doubling. Multiplying by 4 is two doubles, because 4 = 2 × 2. Multiplying by 8 is three doubles, because 8 = 2 × 2 × 2. If you can double a number, you can reach the 2s, 4s, and 8s without a separate fact for each one.
6 × 4. First double 6: 6 × 2 = 12. Double that result: 12 × 2 = 24. Two doubles make ×4, so 6 × 4 = 24. You did not add 6 four times.
- Double the number once for ×2.
- Double that result for ×4.
- Double once more for ×8.
- Stop when you have doubled as many times as the factor needs.
7 × 4: 7 × 2 = 14, then 14 × 2 = 28. 6 × 8 needs one more double after 24: 24 × 2 = 48, so 6 × 8 = 48. 9 × 4: 9 × 2 = 18, then 18 × 2 = 36.
Watch out
- Doubling only once for a ×4 fact. ×4 needs two doubles.
- Adding 4 instead of doubling twice.
- Doubling a third time when the problem is only ×4.
What is 7 × 4?
7 × 2 = 14, then 14 × 2 = 28.
What is 6 × 8?
6 × 2 = 12, 12 × 2 = 24, and 24 × 2 = 48. Three doubles make ×8.
Math practice for Doubling Strategy
Multiply by 2
Practice this