What you need to know
By Year 4 you need written methods that work for any numbers, not just the ones you can do in your head. For multiplying we use short multiplication (working in columns and carrying) and for dividing we use short division (sometimes called the bus-stop method). Both rely on knowing your times tables to 10 × 10, so keep those sharp.
Short multiplication. Line the numbers up in columns. Multiply the ones digit first, then the tens, then the hundreds. If a product is 10 or more, write the ones digit and carry the tens digit to the next column, where you add it on after multiplying.
46 × 3
- Write 46 with 3 underneath, lined up in the ones column.
- Multiply the ones: 6 × 3 = 18. Write 8 and carry 1 (ten).
- Multiply the tens: 4 × 3 = 12, then add the carried 1 to make 13. Write 13.
- Answer: 46 × 3 = 138.
- Estimate to check: 46 is close to 50, and 50 × 3 = 150. 138 is close, so it is sensible.
237 × 4
- Ones: 7 × 4 = 28. Write 8, carry 2.
- Tens: 3 × 4 = 12, plus the carried 2 = 14. Write 4, carry 1.
- Hundreds: 2 × 4 = 8, plus the carried 1 = 9. Write 9.
- Answer: 237 × 4 = 948. Estimate: 240 × 4 = 960, so 948 is sensible.
Short division. Write the number you are dividing by (the divisor) outside the bus stop and the number being divided inside. Work from the left, one digit at a time, asking how many times the divisor fits. Write the answer on top. Any amount left over is carried to the front of the next digit.
95 ÷ 4
- 4 into 9 goes 2 times (2 × 4 = 8) with 1 left over. Write 2 above the 9 and carry the 1 to make 15.
- 4 into 15 goes 3 times (3 × 4 = 12) with 3 left over. Write 3 above the 5.
- Answer: 95 ÷ 4 = 23 remainder 3.
- Check with multiplication: 23 × 4 = 92, and 92 + 3 = 95.
138 ÷ 6
- 6 into 1 does not go, so look at the first two digits: 6 into 13 goes 2 times (12) with 1 left over. Write 2 above the 3 and carry the 1 to make 18.
- 6 into 18 goes exactly 3 times. Write 3 above the 8.
- Answer: 138 ÷ 6 = 23.
- Check: 23 × 6 = 138.
| Problem | Calculation | Sensible answer |
|---|
| 26 pencils are shared equally among 4 students. How many does each student get? | 26 ÷ 4 = 6 r 2 | 6 pencils each (2 left over) |
| 26 students travel 4 to a car. How many cars are needed? | 26 ÷ 4 = 6 r 2 | 7 cars (the 2 extra students still need a car) |
| $26 is shared equally between 4 people. How much each? | 26 ÷ 4 = 6.5 | $6.50 each |
Common mistake: in short multiplication, adding the carried digit before multiplying. In 46 × 3 the tens column is (4 × 3) + 1 = 13, not (4 + 1) × 3 = 15. Multiply first, then add the carry.
Common mistake: in short division, skipping a zero. For 612 ÷ 3: 3 into 6 goes 2; 3 into 1 goes 0 (write the 0 and carry the 1); 3 into 12 goes 4. The answer is 204, not 24. Check: 204 × 3 = 612.
Check yourself
- 38 × 4 = ?
- 125 × 6 = ?
- 96 ÷ 3 = ?
- 87 ÷ 5 = ? (give the remainder)
- 156 ÷ 4 = ?
- 29 people are seated at tables of 6. How many tables are needed?
Answers: 1. 152 2. 750 3. 32 4. 17 remainder 2 (17 × 5 = 85, 85 + 2 = 87) 5. 39 6. 5 tables (29 ÷ 6 = 4 r 5, and the 5 extra people need another table)