Multiplication & division
Column Multiplication
The column method is an efficient way to multiply a whole number up to 1000 by a 1-digit number. You estimate first, then multiply column by column, carrying as you go.
Estimate first
1. Round each number to make an easy calculation. 2. For 346 x 9, round to 350 x 10 = 3500. 3. Your final answer should be close to this estimate. If it is not, check your work.
Multiply column by column
1. Write the number with the 1-digit multiplier underneath the ones. 2. Work from right to left: multiply the ones first, then the tens, then the hundreds. 3. If a column makes 10 or more, write the ones digit and carry the rest to the next column. 4. Add any carried amount to the next column's product.
Check against your estimate
1. Read your final answer. 2. Compare it with the estimate you made at the start. 3. If they are close, your answer is sensible.
Worked examples
Estimating a product
- You want to work out 346 x 9.
- Round 346 to 350 and 9 to 10.
- Multiply the rounded numbers: 350 x 10 = 3500.
Answer: A good estimate is 3500.
Multiplying with carrying
- Work out 346 x 9, right to left.
- 6 x 9 = 54: write 4, carry 5 tens.
- 40 x 9 = 360, add 50 = 410: write 1 in the tens, carry 4 hundreds.
- 300 x 9 = 2700, add 400 = 3100.
- Check: 3114 is close to the estimate 3500.
Answer: 346 x 9 = 3114.
Where you see this in real life
- Working out how much fuel a plane needs by multiplying fuel burned each hour by the journey time.
- Finding the total cost of 8 ski passes that each cost the same amount.
- Working out the total mass of many identical screws or parts.
Key words
- Product
- The answer when you multiply two numbers together.
- Estimate
- A sensible guess made by rounding, used to check an answer.
- Carry
- Moving a ten or hundred into the next column when a column total is 10 or more.