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We are given A speaks before B, B before C and C before D

From the 6 slots, we can choose any 4 slots but there is only one way of placing them in those 4 slots that satisfy the above criterion. This can be done in 6C4= 15 ways.

The other two can be placed in 2! ways

total ways =15*2=30

Therefore, Option D
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Total number of ways of 6!=720
Constraint is that 4 of them have a specific sequence i.e. A>B>C>D.

hence answer is 720/4!=30

D
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Order ABCD.. Other two speakers X & Y
now 5 places available. so if X takes any of 5, Y will take any of 4. total 20
now together also they occupy slots as XY or YX. so 5*2=10
total = 20+10 =30

Ans D
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We use combination to pick the 4 distinct from the total 6 and arrange the other two in either of the remaining positions
6C4X2! = 15X2= 30
Ans D
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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Lets start by naming 6 position :- A B C D E X Y

We know A will perform before B, B before C & C before D
only possible option between these 4 people can be { A B C D}
then we have 2 people x and y which can be placed anywhere cause we don't have any restrictions.

then by marking spots between the spaces we can find the number of available space for X and Y
ie, | A | B | C | D |

all the lines above displays number of spaces available for X and Y

Case 1 :-
X and Y are separated :- 5C2 * 2!
Case 2
X and Y together :- 5C1 *2!

IMO D
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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
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A,B,C,D = 4!
Total 6!. So 6!/4! = 30
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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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Alex, Bruno, Carla and Denise are in a fixed order that can't be changed. The only thing that can be arranged is the arrangement of the other two speakers. So we'll arrange them in different ways.

Can think of it as seats each person is taking up.

A B C D x y

We need to find how many ways you can arrange 2 people in 6 seats, because A B C and D are not moving around. This is:

\(6C2=\frac{6*5}{2}=15\)

For each of these arrangements, you can reverse the order of x and y as well because order matters in this situation. Thus:

\(15*2=30\)

Answer is D.
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Let the 4 members be identified by their initials, so A, B, C, D and the other 2 members be X & Y.

Suppose we only have the 4 members to be arranged in the needed order, we can do so only in 1/4! = 1/24 ways.

So, when there are 6 members there will be only 1/24 th of all the schedule that will be in the required order,
therefore 6! *1/24 = 30 ways
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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They can appear in any of 4
A<B<C<D
Slot1= 6choices, slot 2= 5 choices, slot3= 4 choices, slot 4= 3 choices, slot 5= 2 choices and slot 6=1 choice
so 6x5x4x3x2x1= 720
Position 1=4 choices, 2=3, 3=2, 4=,1
4x3x2x1=24
720/24=30
Answer is 30
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The order is A<B<C<D
Let remaining two speakers be X and Y

There are 4 people out of 6 whose relative order is fixed.
Number of ways to choose 4 positions from 6 is \(6C4\) = 15
In each of these 15 choices, there is only 1 way to assign A,B,C,D in the required order.
X and Y can be placed in the remaining 2 slots = 2! ways = 2
Total ways = 15*2 = 30 ways

(D) is the answer
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total 6 speakers
6 slots
now a,b,c,d needs to sit in certain scenario. a<b, b<c, c<d
we need to find how many ways can we find 4 slots for them.
6C4= 15 ways.
now the remaining 2 peole can seat in just 2 ways.
so total- 15*2= 30

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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We can imagine this problem like a container of length 6, with always 2 slots free

[*, A , B , * , C , D] so we can think about the number of ways that we can place the 2 asteriscs * in a container of length 6.
disp = 6!/(6-2)! = 30

There are not other possibilities since the 4 remaining elements A,B,C,D must be in one and only one order for every disposition of the 2 asteriscs.

IMO D
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1. Use nCr fórmula
2. n=6 and r=4
3. Do the calculation 6!/4!
4. The result is 30
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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 us fill it in this way
_A_B_C_D_

in blank spaces we need to arrange E F in multiple ways. That will give us the answer
in case 1 ; E and F are together
there 5 blanks so 5 ways to fill EF , and interchanging there order tp FE we get anothr 5 ways total 10
now in case 2; E and F are seperate
so ways to postion E = 5 ( 5 blanks) and once we decide postion of E then ways to position F is 4 ways ( one apart from where E is kept)
so toal cominaton is 4*5 = 20

total ways 10 + 20 = 30
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Case 1:

Other two speakers sit next to each other

_, _, A, B, C, D

each position has 2 ways and there are 5 places (including before A and after D) = 10 ways

Case 2:
Other two speakers sit besides A or B or C or D

_, A, _ B, _, C, _, D _

\(5p2 = 5 * 4 = 20 \)


Total = 10 + 20 = 30 ways

Ans: Option D
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There are few cases that needs to be created in order to solve this problem. First Group Alex , Bruno , Carla , Denise together. So first we have three objects , this above group , speaker 5 , speaker 6. Total no of ways in which they can be arranged is 3!. Now unbox them and create alternate spaces starting front from Alex. Like speaker 5 can be before Alex , Speaker 6 can be after Carla. So there will be (5C2)*2! ways to arrange it. Now it also includes one of the arrangement which is Speaker5/6 before and after Alex , Denise. So subtract 2!.

So , final arranged ways is 3!+(5C2)*2!-2 = 26-2 = 24.
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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