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My three-digit code is 023. Reckha can't choose a code that is the same as mine in two or more of the three digit-positions. Reckha can otherwise choose any three-digit code where each digit is in the set . How many codes are available for Reckha?

 Jan 8, 2022
 #1
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Which digits are in "the set"?

 

If the set consists of all ten digits, then there are 1000 possible combinations.

Of these 30 are not allowed:  02x, 0x3, x23 (where x is any of the ten digits.

In this case there are 1000 - 30 allowable combinations.

 Jan 8, 2022

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