You need a $3$ -digit passcode to unlock a lock .

If you know that :

$\boxed{548}$ , One of the numbers is correct and in the right place.

$\boxed{530}$ , There is no correct number here.

$\boxed{157}$ , There are two correct numbers but they are in the wrong place.

$\boxed{806}$ , There is one correct number but it is in the wrong place.

$\boxed{647}$ , There is one correct number but it is in the wrong place.

Then , what is the $3$ -digit passcode ?

$\boxed{148}$
$\boxed{147}$
$\boxed{741}$
$\boxed{718}$

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From clue (2), we know that there is no 5 in the number. Then clue (3) tells us that 1 and 7 are both in the passcode. Now, using clue (1), this means that the passcode is either $741$ or $718$ . Either clue (4) or clue (5) -- we only need one of them -- tells us that $\boxed{718}$ is indeed the correct code.