Multiply by One Digit
Multiplying by one digit means multiplying a larger number — like 24 or 236 — by a single-digit number such as 3 or 6. In Year 4 (ACARA v9), students use efficient strategies rather than repeated addition: the most useful is partitioning, where you break the big number into place-value parts, multiply each part, then add. The key idea: 4 x 26 becomes 4 x 20 plus 4 x 6, which is 80 + 24 = 104 — easier facts combined to solve a harder one. This builds directly on times-table knowledge and prepares children for written multiplication and multiplying by two digits.
Worked examples
Multiply 3 x 24 using partitioning.
Split 24 into 20 and 4. Multiply each: 3 x 20 = 60 and 3 x 4 = 12. Add: 60 + 12 = 72.
Answer: 72
Multiply 5 x 36.
Split 36 into 30 and 6. 5 x 30 = 150 and 5 x 6 = 30. Add: 150 + 30 = 180.
Answer: 180
Multiply 4 x 213.
Split 213 into 200, 10 and 3. 4 x 200 = 800, 4 x 10 = 40, 4 x 3 = 12. Add: 800 + 40 + 12 = 852.
Answer: 852
Real-world: a cinema row has 32 seats. How many seats in 6 rows?
Work out 6 x 32. Split 32 into 30 and 2: 6 x 30 = 180 and 6 x 2 = 12. Add: 180 + 12 = 192.
Answer: 192 seats
Tips
- •Break the big number into place-value parts. Splitting 47 into 40 and 7 turns one hard multiplication into two easy ones you can add together.
- •Multiply the tens and the ones separately, then add. Keeping the parts lined up by place value stops the numbers getting muddled.
- •Common mistake to watch for: children sometimes forget the place value and treat the 4 in 47 as a 4, not 40 — so 3 x 47 loses 90. Remind them the 4 stands for 40, so 3 x 40 = 120, not 12.
- •Estimate first to check. Rounding 6 x 32 to 6 x 30 = 180 gives a ballpark, so an answer of 192 looks right but 84 would not.