part a) can we repeat "a" in any of the 6 positions for the string? in other words, is it possible to have the string "aaaaaa"?
Yes. That string contains at least one a.
So does this mean the answer would be 26^5? (At least for part a)
No, from my understanding, I believe you would find the total amount of ways without using the letter a which would be 25^6 and then subtract that from the total ways with a which is 26^6. --Krwade 21:11, 4 February 2009 (UTC)
for part d..I don't understand why the answer is 6 choosing 2 when a is to the left of b. I do, however, understand 24*23*22*21...just don't understand the 15 I guess. I just don't understand...
In part d, look at it like this: We have a and b somehow arranged in a group of six letters where a must always come before b. a and b act as dividers creating three bins that the other four letters can fall into. giving us 4things + 3bins - 1 choose 4things. --User:mturczi
