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Counting all 2-distinct-digit occurrences from 4-digits combinations

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Intern
Joined: 02 Nov 2017
Posts: 1
Counting all 2-distinct-digit occurrences from 4-digits combinations  [#permalink]

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02 Nov 2017, 11:13
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Currently I'm facing a problem to find out the formula to count 2 distinct digits say X and Y from a 4-digit combinations, where each digit can be range from 0 to 9, programming solution give me an answer of 974

I'm able to find out if to count 1 digit say X from a 4-digit combinations: $$10^4 - 9^4 = 1000 - 6561 = 3439$$

I've tried to read some articles, but a bit too dumb to understand how it works. I'm trying to get my colleague help too, it seem not so easy to get the formula, also not sure the programming answer is correct.

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This discussion does not meet community quality standards. It has been retired.

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Math Expert
Joined: 02 Sep 2009
Posts: 49300
Re: Counting all 2-distinct-digit occurrences from 4-digits combinations  [#permalink]

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02 Nov 2017, 23:35
whislai wrote:
Currently I'm facing a problem to find out the formula to count 2 distinct digits say X and Y from a 4-digit combinations, where each digit can be range from 0 to 9, programming solution give me an answer of 974

I'm able to find out if to count 1 digit say X from a 4-digit combinations: $$10^4 - 9^4 = 1000 - 6561 = 3439$$

I've tried to read some articles, but a bit too dumb to understand how it works. I'm trying to get my colleague help too, it seem not so easy to get the formula, also not sure the programming answer is correct.

--== Message from the GMAT Club Team ==--

THERE IS LIKELY A BETTER DISCUSSION OF THIS EXACT QUESTION.
This discussion does not meet community quality standards. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.

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Re: Counting all 2-distinct-digit occurrences from 4-digits combinations &nbs [#permalink] 02 Nov 2017, 23:35
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