If A1, A2, A3, A4, ..... A10 are speakers for a meeting and A1 always speaks aft

CuriousTab

Home Aptitude

Discussion

Home ‣ Aptitude ‣ Permutation and Combination See What Others Are Saying!

Question
If A1, A2, A3, A4, ..... A10 are speakers for a meeting and A1 always speaks after, A2 then the number of ways they can speak in the meeting is
Options
A. 9!
B. 9!/2
C. 10!
D. 10!/2

Correct Answer

10!/2

Explanation

As A1 speaks always after A2, they can speak only in 1st to 9th places and

A2 can speak in 2nd to 10 the places only when A1 speaks in 1st place

A2 can speak in 9 places the remaining

A3, A4, A5,...A10 has no restriction. So, they can speak in 9.8! ways. i.e

when A2 speaks in the first place, the number of ways they can speak is 9.8!.

When A2 speaks in second place, the number of ways they can speak is 8.8!.

When A2 speaks in third place, the number of ways they can speak is 7.8!. When A2 speaks in the ninth place, the number of ways they can speak is 1.8!

Therefore,Total Number of ways they can speak = (9+8+7+6+5+4+3+2+1) 8! = $\frac{9}{2} (9 + 1) 8!$ = 10!/2