Multiplication by 111
To multiply mentally by 111, follow these steps:
- Write the last digit of the number.
- Add the last digit to the digit on its left; write the
last digit of the sum and carry if necessary.
- Add the last digit to the digit on its left and to the
next digit on its left; add the carry from the previous
steps. Write the last digit of the sum and carry if
necessary.
- Move one digit to the left and add the two digits on its
left. Add any carry. Write and carry.
- Continue moving one digit to the left until the end of
the number.
Example:
24 × 111 =
| Write the 4 |
4 |
| Add 4 and 2. 4 + 2 = 6. |
64 |
| Add 4 and 2 and 0. 4 + 2 + 0 = 6 |
64 |
| Move to the 2. |
|
| Add 2 and 0 and 0. 2 + 0 + 0 = 2 |
2664 |
24 × 111 = 2664
Example:
453 × 111 =
| Write the 3. |
3 |
|
| Add 3 and 5. 3 + 5 = 8 |
83 |
|
| Add 3 and 5 and 4. 3 + 5 + 4 = 12 |
283 |
(carry 1) |
| Move to the 5. |
|
|
| Add 5 and 4 and 0 and the carry. 5 + 4 +
0 + 1 = 10 |
0283 |
(carry 1) |
| Move to the 4. |
|
|
| Add 4 and 0 and 0 and the carry. 4 + 0 +
0 + 1 = 5 |
50283 |
|
453 × 111 = 50283
|
