Same product, new shape
Today I can explain why the product stays the same when one factor is doubled and the other is halved.
A Look back3 min
- 1.
34 ÷ 10 =
- 2.
5 × 4 =
- 3.
7 × 10 =
B Watch me, then you4 min
Sam sets out 6 rows of 5 stickers. He wants fewer rows. Does the total change?
Sam has 6 rows of 5, which is 30 stickers.
Halve the 6 rows to 3, and double the 5 to 10.
3 rows of 10 is also 30 stickers, so the total stays the same.
- 1.
8 × 5 = 4 ×
C Your turn5 min
Double or halve one factor, and do the opposite to the other. You may need to do this more than once. Then find the missing number.
- 1.
5 × 12 = 10 ×
- 2.
5 × 12 = 20 ×
- 3.
5 × 12 = 2.5 ×
- 4.
16 × 25 = 8 ×
Say it out loud: Which factor did you halve, and which did you double, in each row? What stayed the same?
D Spot the mistake2 min
- 1.
What is 12 × 10?
E Think deeper4 min
This rectangle has 4 rows of 6, so 4 × 6 = 24.
- 1.
Use doubling and halving to write a different multiplication that equals 4 × 6. Then explain in one sentence why the product is still 24.