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One counting problem

 
 
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One counting problem
WangHenry - 2025年08月5日 Tuesday 17:20
 

How many six digit numbers are there that have exactly one pair of digits that differ by 5? Can anyone give me a hand? Thanks.

 
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Re: One counting problem
AdminZIML - 2025年08月6日 Wednesday 03:03
 

There are $5$ possible pairs: $(0,5)$, $(1,6)$, $(2,7)$, $(3,8)$, and $(4,9)$.  Only one of these pairs have both digits appear, non-repeating.  For each of the other pairs, only one digit can appear, repeating allowed. Also consider $0$ cannot be the first digit.

 
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