permutations-How many of these four digit numbers are odd?

G

Guest

Guest
My questions is,

How many four digit numbers can you form with the digits 1,2,3,4,5,6, and 7, if no digit is repeated?

I know how to do this part, I did 7P4= 840,

but for this question, I can't remember how to do these anymore- How many of these four digit numbers are odd?
I remember doing something like subtracting from the total ways (840)..or not..I really can't remember how I did this way back months ago,

...The answer is 480

Thanks if you could help
 
You have 4 odd digits and 3 even digits; so 4/7 * 840 = 480
 
You could also think of it this way:

If the number is odd, there are 4 to choose from: 1,3,5,7

Place one of those at the one's digit in 4 ways.

Then you have 6 digits to choose from for the 10's digit, 5 for the 100's digit and 4 for the 1000's digit.

4*5*6*4=480
 
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