say you have to find how many 4 letter combination's there are of the word "outlook"
how do you do that?
If it where a word with no repeated letters it wouldnt be bad ie 7C4 (Pretty sure) = 7!/(4!3!) = 35
but what is this, maybe it's 6c4 = 6!/(2!2!) = 180? I know that is wrong the answer is 15.