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 From B. Lee Clay

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Multiplying a repeating 2's number by 15

1. Choose a repeating 2's number (222, etc.)
2. Multiply it by 15
3. The product is:
- the first digit is 3
- the next digits are repeating 3's (one fewer than repeating 2's in the original number)
- the last digit is 0

Example:

1. If the first number is 22222:
2. Multiply by 15. The product is:
- the first digit is 3: 3.
- the next digits are repeating 3's (one fewer than repeating 2's in the original number): 3333.
- the last digit is 0: 0.
3. So 22222 × 15 = 333330.

See the pattern?

1. If the first number is 222222:
2. Multiply by 15. The product is:
- the first digit is 3: 3.
- the next digits are repeating 3's (one fewer than repeating 2's in the original number): 33333.
- the last digit is 0: 0.
3. So 222222 × 15 = 3333330.