There are 8 speakers A,B,C,D,E,F,G and H in a conference. A,B and C always speak in alphabetical order. The probability that A,B and C are the first 3 speakers is a/b, where 'a' and 'b' are co-prime, find a+b. This is one among the qstns I found in your video series for probability. I really didn't understand how the total no of outcomes became (8!/6), why can't we take A,B,C as one unit and consider the total no of outcomes to be 6! ?

Because it is a possibility that A,B,C are the 1st 3 speakers. A,B,C will speak in alphabetical order is affirmative.therefore total number of outcomes will be 8!/6

I am not able to understand probability and permutation , combination

please solve 12 th and 11th class ncert math problems ,along with RD sharma book to strengthen your base; to improve further, try solving puzzles in probability puzzles app, it needs regular attention!