Help me do this probability problem

[KahunaHube]

I have this midterm tomorrow, and I can't seem to find out how to answer this question. Can anyone help?

Question:
How many different 7-character passwords are possible when 3 of the characters are letters and 4 are digits? Assume that the repetition of letters and numbers is allowed and that there is no restriction on where the letters or numbers can be placed.

The answer is: 6,151,600,000

All I know is that it isnt 7!(26^3 * 10^4) <-- that number is too large.

Any help is appreciated

Thanks!
-Hubert

 

[z0mb13]

how many letters are there?

 

[KahunaHube]

nm i figured it out
but thanks!

its 26^3 * 10^4 * 7!/(3!4!)

thanks again

-HUbert

 

[Orsorum]

Originally posted by: KahunaHube
nm i figured it out
but thanks!

its 26^3 * 10^4 * 7!/(3!4!)

thanks again

-HUbert

THAT'S what it was. I was playing around with the exact same numbers, just had trouble remembering what to do with the 3!4!.

 

[KahunaHube]

Originally posted by: Orsorum

Originally posted by: KahunaHube
nm i figured it out
but thanks!

its 26^3 * 10^4 * 7!/(3!4!)

thanks again

-HUbert

THAT'S what it was. I was playing around with the exact same numbers, just had trouble remembering what to do with the 3!4!.

yeah me too that was killing my brain cells for a good 5 minutes!