Guess My House
Mac's new house number has three digits. When she challenged her friends to guess it, they tried: 135, 780, 785, and 732.
"That's amazing," Mac said. "You've each guessed exactly one digit correctly and in its right place!"
What is Mac's house number?
The first digit must be 1 or 7. It can't be 7 as only one digit is correct in each guess. So it's 1.
The other digits in guess #1 (i.e. 3 and 5) must be incorrect. Therefore, from guess #3, the second digit is 8.
Guess #4 has a correct digit which must be its third - 2.
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