For a drama, 3 students need to be selected out of 6 students A, B, C,

Question

For a drama, 3 students need to be selected out of 6 students A, B, C, D, E and F. If A is already selected, what is the probability of selecting C also?

A. 0.5
B. 0.2
C. 0.3
D. 0.4
E. 0.1

Are You Up For the Challenge: 700 Level Questions

Regor60 · Answer

Number of ways to select two remaining teammates out of 5

5!/2!3!= 10

With A and C selected, number of ways to select 1 remaining out of 4 = 4

Probability 4/10

Posted from my mobile device

IanStewart · Answer

It's just like lining the remaining 5 students up, and asking the probability "C" is in one of the first 2 places in line -- the answer is just 2/5.

DUMDUM21 · Answer

Since C could selected for either of two remaining spaces, (5C1 + 4C1)/5C2 = 9/20 = .45 and rounding it up gives .5.
Where did I go wrong in this?

Bunuel · Answer

I'm not clear with your approach, so I'll offer another one involving combinations. Maybe that helps.

We need C to be among 2 chosen students out of the remaining 5:

1C1*4C1/5C2 = 4/10 = 0.4. Here, 1C1 represents choosing C, 4C1 represents choosing any from the remaining 4, and 5C2 represents the total number of ways to choose 2 out of 5.

Answer: D.

Dereno · Answer

As A is already selected. We are left with B,C,D,E and F for the remaining 2 spots.

Amongst the 5 members, selecting two gives us 5C2 options = 10.

This is the  total number of cases = 10

The following are the possible cases for selecting 2 out of 5 :  BC, BD, BE, BF, CD, CE, CF, DE,DF, EF

with each letter appearing 4 times,

Probability of selecting C = 4/10 =  0.4

option D

PSKhore · Answer

Probability of selecting C also = 1 - (Probability of not selecting C)

Probability of not selecting C = 4C2/5C2

because we will be selecting the remaining 2 members from 4 (excluding A and C)

1- (6/10) = 1- (3/5)

=2/5

1/5 is 0.2, so 2/5 will be 0.4

For a drama, 3 students need to be selected out of 6 students A, B, C,

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Problem Solving (PS) Questions

For a drama, 3 students need to be selected out of 6 students A, B, C,

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards