Multiplication by 12
To multiply a number by 12, follow these steps:
- Multiply the last digit by 2. Write down the last digit
of this product and carry if necessary.
- Move to the next digit to the left.
- Multiply that digit by 2 and then add that product to the
digit on its right. Finally, add the carry from the
previous steps. Write down the last digit and carry if
necessary.
- Continue to move to the left, multiply by 2, add to the
right, write and carry until you reach the end of the
number.
- At the end, you will have to multiply the leading 0 by 2
and then add to the right.
Example:
31 × 12 =
| Multiply 1 by 2. 1 × 2 = 2. |
2 |
| Move to the left and to the 3. |
|
| Multiply 3 by 2, and then add 1 (the
number on the right). |
|
| (3 × 2) + 1 = 6 + 1 = 7. |
72 |
| Move to the left again, but since there
is no more numbers, you use 0. |
|
| Multiply 0 by 2, and then add 3 (the
number on the right). |
|
| (0 × 2) + 3 = 0 + 3 = 3 |
372 |
31 × 12 = 372.
Example:
917 × 12 =
| Multiply 7 by 2. 7 × 2 = 14. Write 4,
carry 1. |
4 |
(carry 1) |
| Move to the left and to the 1. |
|
|
| Multiply 1 by 2, and then add 7 and add
the carry. |
|
|
| (1 × 2) + 7 + 1 = 10. |
|
|
| Write 0, carry 1. |
04 |
(carry 1) |
| Move to the left and to the 9. |
|
|
| Multiply 9 by 2, and then add 1 and then
add the carry. |
|
|
| (9 × 2) + 1 + 1 = 20 |
|
|
| Write 0, carry 2. |
004 |
(carry 2) |
| Move to the left and to the invisible 0. |
|
|
| Multiply 0 by 2, add 9 and add the carry.
9 + 2 = 11. |
|
|
| Since this is the last number, write the
whole number down. |
11004 |
|
917 × 12 = 11004.
|
