You can use short multiplication if you’re multiplying one number by another that’s in your times tables (up to 12). However, if you want to multiply by a higher number, you need to use long multiplication.
- Write down the numbers one on top of the other with the smaller number on the bottom and a times sign on the left (just as you would normally), then draw three lines underneath to hold three rows of numbers.
- Multiply the top number by the last digit of the bottom number as you would normally.
- Write a zero at the end of the next answer line (to show that you’re multiplying by tens now rather than units).
- Multiply the top number by the next digit of the bottom number, starting to the left of the zero you’ve just added.
- Add the two answer lines together to get the final answer.
- Some people write the tens they’ve carried right at the top of the sum, but that can get very confusing with three lines of answers!
- Don’t forget to add the zero to the second line of your answer. If it helps, you can try writing it down as soon as you set out the sum (and before you’ve even worked anything out).
- At 11+ level, long multiplication will generally be a three-digit number multiplied by a two-digit number, but the method will work for any two numbers, so don’t worry. If you have to multiply two three-digit numbers, say, you’ll just have to add another line to your answer.
Have a go at these questions. Make sure you show your working – just as you’d have to do in an exam.
- 216 x 43
- 17 x 423
- 23 x 648
- 782 x 28
- 127 x 92