How to solve a three-digit code puzzle
Start with what cannot be in the code. Then compare where the remaining digits can go.
This is a separate practice puzzle, not a reveal of today's challenge. It uses the same clue rules: three different digits and exact counts.
| Digits | Clue |
|---|---|
901 | None correct |
025 | None correct |
432 | 1 correct digit, right place |
386 | 2 correct digits, right places |
1. Cross out the impossible digits
The first clue rules out 9, 0, and 1. The second rules out 0, 2, and 5. That leaves 3, 4, 6, 7, and 8 as possible digits.
A digit ruled out by one clue is absent everywhere. You do not need to consider it again in another position.
2. Narrow the choice in 432
We already know that 2 is absent. Exactly one of the other digits is correct and in its right place.
So either 4 is first and 3 is absent, or 3 is second and 4 is absent. Keep both options for now.
3. Compare that with 386
This clue has two correct digits, both in their right places. If 3 were one of them, it would be first.
But 432 says that a correct 3 must be second. It cannot be in both positions, so 3 is absent.
4. Put the code together
With 3 and 2 absent, the correct digit in 432 must be 4, in the first position. With 3 absent from 386, its two correct digits are 8 in the middle and 6 at the end.
The code is:
Check it against every clue. It contains none of 9, 0, 1, 2, or 5. It puts 4 first, 8 second, and 6 third. All four clues agree.
A useful habit
Keep the digit and its position as two separate questions. A correct digit in the wrong place must move; it does not disappear. A clue with one correct digit also rules out the other two.