Long multiplication
You learn to multiply a number by a two-digit number, in two rows.
How to work it out
- Row 1: multiply by the ones digit.
- Row 2: write 0 first, then multiply by the tens digit.
- Add the two rows.
43
×12
86
+430
516
A worked example
43 × 12
- Row 1: 2 × 43 = 86.
- Row 2 starts with a 0: 10 × 43 = 430.
- Add the rows: 86 + 430 = 516.
More examples
56 × 23
- Row 1: 3 × 56 = 168.
- Row 2 starts with a 0: 20 × 56 = 1120.
- Add the rows: 168 + 1120 = 1288.
56
×23
168
+1120
1288
27 × 14
- Row 1: 4 × 27 = 108.
- Row 2 starts with a 0: 10 × 27 = 270.
- Add the rows: 108 + 270 = 378.
27
×14
108
+270
378
Watch out
You forget the 0 at the start of the second row: for 43 × 12 you add 86 + 43 and get 129.
The 1 in 12 is a ten. So you multiply by 10, and that row starts with a 0.
Tips
- The second row starts with a 0, because you are multiplying by tens.
- Estimate first: 43 × 12 is about 40 × 12, so just under 500.
Why it works
43 × 12 is 43 × 2 and 43 × 10. The first row is times the ones, the second row is times the tens. Because the tens are worth ten times as much, that row starts with a 0. Add the two rows and you have the answer.