You can solve it using probability. The probs of getting a was 3/7 then b is 2/6 then 2nd b is 1/5, last a is 2/4. Times all together and you get 1/70? I think it was
I got 7C4 as the total amount =35 And then 2! X 2! = 4 so 4/35
I just did 3*2*1*2 7 6 5 4 for ABBA as that is the probability of each letter in each place. I checked this with 3!*2! 7P4 As this is the amount of ways the ABBA can be arranged by mixing up the A's and B's if that makes any sense. So The total ways you can get ABBA which = 12 (3! * 2! = 12). On the bottom is the total ways of arranging it with any set of 4 letters in any of the 4 places (So you could have CACB etc.) And 7P4 = 840. 12 840 = 1 70 Sorry feel that wasn't worded well but hopefully you can see what I mean.