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How many numbers greater than 5000 can be formed with the digits 3,4,6,8,9 if a digit cannot occur more than once in a number?



Answer :

diene
we can split this into 2 cases:
4-digit numbers and 5-digit numbers
4-digit numbers:
it'll only be greater than 5000 if the first digit is 6, 8, or 9. The other 3 digits can be anything else, so there are a total of 3*4*3*2=72 4-digit numbers
5-digit numbers: all 5-digit numbers are greater than 5000, so there are a total of 5*4*3*2*1 =120 5-digit numbers
the total is 72+120=192 numbers greater than 5000
AL2006
With no upper limit on the numbers, an infinite number of them can be written.

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