Bunuel
A tech conference schedules 6 speakers, including Alex, Bruno, Carla, and Denise, to give presentations in 6 different time slots, one speaker per slot. If Alex must speak earlier than Bruno, Bruno earlier than Carla, and Carla earlier than Denise, in how many different ways can the 6 speakers be scheduled?
A. 6
B. 12
C. 24
D. 30
E. 120
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Let the speakers Alex, Bruno, Carla and Denise be represented as a,b,c,d respectively.
The remaining two speakers be e and f respectively.
so, the 6 speakers are : a,b,c,d,e,f.
The 6 speakers can be arranged in 6! Ways = 6*5*4*3*2*1 = 720 ways.
The four speakers a,b,c,d be arranged in 4! Ways = 4*3*2*1 = 24 ways.
Amongst the 24 ways, ONLY 1 way has a sequence of A> B> C >D.
If among 24 ways, we have 1 case.
so, for 720 ways , the number of cases = (720/24) =
30
Option D