How Many 4-digit Numbers Can Be Formed Using The Digits 0,1,2,3,4,5,6 If Repetition Of Digits Is Not Allowed?


4 Answers

Oddman Profile
Oddman answered
There are (7!)/(7-4)! = 7*6*5*4 permutations of 7 numbers taken 4 at a time. That's 840. Some of the numbers will have a leading zero.

If you don't allow a leading zero, there are 6*6*5*4 = 720 possible 4-digit numbers.

The first couple are 0123, 0124, ...
The last couple are ..., 6542, 6543.

The set of numbers not having leading zeros begins with 1023, 1024, ...
Anonymous Profile
Anonymous answered
If numbers can be repeated how many 4 digit numbers can be formed using the numbers 4,5,7,8,9

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