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Probability

This topic has 2 expert replies and 2 member replies
prernamalhotra Senior | Next Rank: 100 Posts Default Avatar
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Probability

Post Mon Jun 16, 2014 6:14 am
A small company employs 3 men and 5 women. If a team of 4 employees is to be randomly selected to organize the company retreat, what is the probability that the team will have exactly 2 women?

1) 1/14
2) 1/7
3) 2/7
4) 3/7
5) 1/2

Thank you,
Prerna

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GMATinsight Legendary Member
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Post Mon Jun 16, 2014 7:56 am
The answer will staraight away be this way

Probability = (favorable outcome) / (Total Outcome)
= (3C2 x 5C2)/(8C4) = 30/70 = 3/7 ANSWER

[ 3C2 refers the no. of ways of selecting 2 men out of 3 men and 5C2 refers the number of ways of selecting 2 Women out of 5 Women ]

[8C4 refers to the total number of ways of selecting 4 out of 8 individuals]

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Top Reply
Post Mon Jun 16, 2014 7:14 am
Quote:
A small company employs 3 men and 5 women. If a team of 4 employees is to be randomly selected to organize the company retreat, what is the probability that the team will have exactly 2 women?

A) 1/14
B) 1/7
C) 2/7
D) 3/7
E) 1/2
When a probability problem uses the word exactly, we can apply the following reasoning:
P(exactly n) = P(one way) * all possible ways.

Let W = woman and M = man.

P(one way):
One way to get 2 women and 2 men is WWMM.
P(1st person is W) = 5/8. (8 people, 5 of them W.)
P(2nd person is W) = 4/7. (7 people left, 4 of them W.)
P(3rd person is M) = 3/6. (6 people left, 3 of them M.)
P(4th person is M) = 2/5. (5 people left, 2 of them M.)
Since we want all of these events to happen together, we multiply the fractions:
P(WWMM) = 5/8 * 4/7 * 3/6 * 2/5 = 1/14.

All possible ways:
Any arrangement of WWMM will yield exactly 2 W and 2 M.
Thus, the result above must be multiplied by the number of ways to ARRANGE the 4 elements WWMM.

The number of ways to arrange 4 elements = 4!.
But WWMM includes IDENTICAL elements.
When an arrangement includes identical elements, we must divide by the number of ways each set of identical elements can be arranged.
The reason:
When the identical elements swap places, the arrangement DOESN'T CHANGE.
Here, we must divide by 2! to account for the two identical W's and by another 2! to account for the two identical M's:
4!/(2!2!) = 6.

Thus:
P(exactly 2 W) = 1/14 * 6 = 3/7.

The correct answer is D.

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GMATinsight Legendary Member
Joined
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Posted:
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Upvotes:
205
Post Mon Jun 16, 2014 7:56 am
The answer will staraight away be this way

Probability = (favorable outcome) / (Total Outcome)
= (3C2 x 5C2)/(8C4) = 30/70 = 3/7 ANSWER

[ 3C2 refers the no. of ways of selecting 2 men out of 3 men and 5C2 refers the number of ways of selecting 2 Women out of 5 Women ]

[8C4 refers to the total number of ways of selecting 4 out of 8 individuals]

_________________
Bhoopendra Singh & Sushma Jha - Founder "GMATinsight"
Testimonials e-mail: info@GMATinsight.com I Mobile: +91-9999687183 / +91-9891333772
To register for One-on-One FREE ONLINE DEMO Class Call/e-mail
One-On-One Private tutoring fee - US$40 per hour & for FULL COURSE (38 LIVE Sessions)-US$1000

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Post Mon Jun 16, 2014 7:14 am
Quote:
A small company employs 3 men and 5 women. If a team of 4 employees is to be randomly selected to organize the company retreat, what is the probability that the team will have exactly 2 women?

A) 1/14
B) 1/7
C) 2/7
D) 3/7
E) 1/2
When a probability problem uses the word exactly, we can apply the following reasoning:
P(exactly n) = P(one way) * all possible ways.

Let W = woman and M = man.

P(one way):
One way to get 2 women and 2 men is WWMM.
P(1st person is W) = 5/8. (8 people, 5 of them W.)
P(2nd person is W) = 4/7. (7 people left, 4 of them W.)
P(3rd person is M) = 3/6. (6 people left, 3 of them M.)
P(4th person is M) = 2/5. (5 people left, 2 of them M.)
Since we want all of these events to happen together, we multiply the fractions:
P(WWMM) = 5/8 * 4/7 * 3/6 * 2/5 = 1/14.

All possible ways:
Any arrangement of WWMM will yield exactly 2 W and 2 M.
Thus, the result above must be multiplied by the number of ways to ARRANGE the 4 elements WWMM.

The number of ways to arrange 4 elements = 4!.
But WWMM includes IDENTICAL elements.
When an arrangement includes identical elements, we must divide by the number of ways each set of identical elements can be arranged.
The reason:
When the identical elements swap places, the arrangement DOESN'T CHANGE.
Here, we must divide by 2! to account for the two identical W's and by another 2! to account for the two identical M's:
4!/(2!2!) = 6.

Thus:
P(exactly 2 W) = 1/14 * 6 = 3/7.

The correct answer is D.

_________________
Mitch Hunt
GMAT Private Tutor
GMATGuruNY@gmail.com
If you find one of my posts helpful, please take a moment to click on the "Thank" icon.
Available for tutoring in NYC and long-distance.
For more information, please email me at GMATGuruNY@gmail.com.

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