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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
