I need to find how many four digit numbers can be made using exactly 2 different digits. ALL DIGITS FROM 1 TO 9 CAN BE USED. NOT JUST 1 AND 0
How many 4 digit numbers can be made with exactly 2 different digits
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combinatorics
permutations
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0Are leading zeros allowed, as in `0220`? – 2012-11-20
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0yes zeroes can be the starting digit – 2012-11-20
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1I think you mean all digits from 0 (not $1$) to $9$. And you don't need to shout. – 2012-11-20
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5You should make some effort yourself. Having people feed you answers here before you've even engaged your brain will not help you learn anything. – 2012-11-20