Unique letter combinations are 26
two letter combinations are = 26c2 = 26X25/2 = 13X25 = 325
two letter code where two letters are same = 26
total combinations = 26+325-26 = 325
answer should be 325
Would you say AC and CA are different codes or same?
I think you will agree that they are different codes. Hence you do not use the combination formula here (26C2) because it only selects 2 different letters out of the 26 letters.
So how do you solve this question? You can do it in two different ways:
You select 2 different letters and then arrange them.
26C2 * 2! = 650
You use basic counting principle. (Check out: http://www.veritasprep.com/blog/2011/10 ... inatorics/
26*25 = 650
The number of one letter codes is 26 so total = 650 + 26 = 676
I agree with you and understood your point. however in one of kaplan
CAT the OA is porvided as 351. Please see the attachment. Please anyone explain why OA is 351
Kaplan CAT.PNG [ 68.02 KiB | Viewed 1021 times ]
-------Analyze why option A in SC wrong-------