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We call a number peachy if every digit in the number is either a  or next to a  For example, the numbers 333, 83  and 303 are all peachy, but the numbers   32223, 786, 340 and 3990 are not peachy.

How many positive 2-digit numbers are peachy?
 

 Oct 9, 2022
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By Inclusion-Exclusion, the answer is 25.

 Oct 10, 2022

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