Idea 24of 24Builds onShare the remainder too
Check a division by multiplying
How can you be sure a division is right?
Today you'll discover
- which multiplication undoes a division
- where the remainder goes
- how one check catches a slip
Think first336 ÷ 14 = 24. Is it right?
Which multiplication checks that 336 ÷ 14 = 24?
Decide first, then press Next. Multiply back and see if you land on the start.
The finished area model for 336 ÷ 14 = 24, then a check line under it: 24 × 14 = 336. Then the model for 250 ÷ 12 = 20 R10 with the 10 left over marked, and the check 20 × 12 + 10 = 240 + 10 = 250. The last step shows 500 ÷ 24 = 20 R20.
See the whole ideathe big idea and the key word, in one place
The big idea
Check a division by multiplying back: quotient times divisor, plus any remainder, is the dividend.
Checking 500 ÷ 24
Multiply back, then add the leftover.
- 500 ÷ 2420 R20
- 20 × 24480
- + 20500
Where it goes nextIt works the other way too: 846 ÷ 18 should give back 47, because 47 × 18 = 846.
Key word
- inverse operation
- an operation that undoes another: dividing undoes multiplying, and multiplying undoes dividing
Ready to use it?
- Check a division by multiplying back.
- Add the remainder back in when you check.