Question 1135938: how many positive odd numbers can be formed from the digits 2,3,4,5,6 if no digit is to be repeated in a given number
48
120
130
None
Answer by math_helper(2461)   (Show Source):
You can put this solution on YOUR website! 130
The answer assumes you can have one, two, three, four, or five digit numbers.
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For one digit numbers: 3 and 5 ---> 2 numbers
Two digit numbers: 4C1 * 2 ---> 8 numbers (breakdown: 4C1 is the number of ways of choosing, say, one of {2,3,4,5} for two digit numbers ending with 3, double that for the 5 replacing the ending value (3 & 5 swapped)).
Three digit numbers: 4C2 * 2! * 2 --> 24 numbers
Four digit numbers: 4C3 * 3! * 2 --> 48 numbers
Five digit numbers: 4C4 * 4! * 2 --> 48 numbers
2+8+24+48+48 = 130
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