Multiplication by 11
To multiply any 2-figure number by 11 we just put the total of the two figures between the 2 figures.
- 26 x 11 = 286
Notice that the outer figures in 286 are the 26 being multiplied. And the middle figure is just 2 and 6 added up.
- So 72 x 11 = 792
For bigger numbers
234 x 11 = 2574
We put the 2 and the 4 at the ends.
We add the first pair 2 + 3 = 5.
And we add the last pair: 3 + 4 = 7.
We add the first pair 2 + 3 = 5.
And we add the last pair: 3 + 4 = 7.
To multiply a two-digit number by 111, add the two digits and if the sum is a single digit, write this digit Two Times in between the original digits of the number. Some examples:
- 36 x 111= 3996
- 54 x 111= 5994
The same idea works if the sum of the two digits is not a single digit, but you should write down the last digit of the sum twice, but remember to carry if needed as illusrated in example below
- 57 x 111= 6327
Because 5+7=12, but then you have to carry the one twice.
For 3 digit numbers
Carry if any of these sums is more than one digit.
Thus 123x111 = 1 | 3 (=1+2) | 6 (=1+2+3) | 5 (=2+3) | 3
Carry if any of these sums is more than one digit.
Thus 123x111 = 1 | 3 (=1+2) | 6 (=1+2+3) | 5 (=2+3) | 3
Similarly,
- 241 x 111= 26751
For an example where carrying is needed
- 352 x 111= 39072
3 | 8 (=3+5) | 10 (=3+5+2)| 7 (=5+2)| 2
= 3 | 8 | 10 | 7 | 2 = 3 | 9 | 0 | 7 | 2
= 39072
= 3 | 8 | 10 | 7 | 2 = 3 | 9 | 0 | 7 | 2
= 39072