vanillagrown
Jan 27, 2008, 05:22 PM
How many different four letter passwords can be formed from the A, B, C, D, E, F, and G if no repetition of letters is allowed?
PolluxCastor
Jan 27, 2008, 05:23 PM
This can be solved using permutations.
jiten55
Jan 27, 2008, 11:52 PM
Look at it like this:
First letter of the password can be selected in 7 ways, then Second in 6 ways, then 3rd in 5 ways, then fourth in 4 ways.
Hence: 7*6*5*4 = 840
OR
Formula for permutations of r objects out of n
= nPr = n!/(n -r)! = 7!/3! = 7*6*5*4 = 840