In a club, 75% of the members are men, and 50% of them are the only...

Question

In a club, 75% of the members are men, and 50% of them are the only engineers in the club. If total number of members in the club is 40 and two of them are selected at random. Then what is the probability that at least one of them is a male or an engineer?

A.

B.

C.

D.

E.

A.   \frac{9}{156} 
 B.   \frac{24}{39} 
 C.   \frac{3}{4} 
 D.   \frac{7}{8} 
 E.   \frac{147}{156}

https://e-gmat.com/blogs/wp-content/uploads/2018/08/Quant-workshop_Webinar-e1533628475738.jpg

EgmatQuantExpert · Accepted Answer

Solution 
  Given:  
 • Total members of the club = 40
• 75% of the total members are men = 0.75 * 40 = 30
• 50% of the men are engineers = 0.5 * 30 = 15, and these are the only engineers in the club

To find:  
 • If two members are selected at random, what is the probability that at east one of them is a male or an engineer

Approach and Working:   
 • P(at least one male or engineer) = 1 – P(no male or engineer)
 o P(no male or engineer) = P(selecting two women) =  \frac{^{10}C_2}{^{40}C_2} = \frac{9}{156}

• Thus, P(at least one male or engineer) =  1- \frac{9}{156} = \frac{147}{156}

Hence the correct answer is Option E.

Answer: E

https://e-gmat.com/blogs/wp-content/uploads/2018/08/Ability-Quiz-AT-e1533292152363.png

pandeyashwin · Answer

No of male non E (M) = 15 
No of male E (ME)= 15
No of female (F)= 10
No of ways to select 2 people = 40c2 = 780\

No of ways to select at least 1 male or engineer = 
1M x 1F = 15c1 x 10c1 = 150
1ME x 1F = 15c1 x 10c1 = 150
1M x 1ME = 15c1 x 15c1 = 225
2M = 15c2 = 105
2ME = 15c2 = 105

735/780 = 147/156

Option E

kiranteja93 · Answer

Hi guys,
Can anyone explain the ostensible logical confusion in the answer strategy.
The previous answer used 1 - P(Neither) Logic.
This would mean that the calculation is for either scenario (one can visualize easily in a Venn Diagram )
In this particular case , as you know the engineer area or circle is completely included within the Men's circle,since all engineers are men.
The entire intersection is part of Engineer circle.
 The either circle is the Men's circle (Please correct me here if I am wrong)
So I calculated it as 30C2 / 40C2 and got it as 87/156.

My question: Why is this different from 1- P(Neither case).

EgmatQuantExpert · Answer

Hi  kiranteja93 ,

You have missed one case, where we can select one from the 30 members, who are male, set and the other member from the remaining 10 members set. Since, we are asked to find out the probability of  at least one  male or engineer.

The probability of selecting one member from 30 set and other from the remaining 10 set would be  ^{30}C_1 * ^{10}C_1/^{40}C_2 = \frac{60}{156}

Thus, answer =  \frac{87}{156} + \frac{60}{156} = \frac{147}{156}

Regards,

shashankism · Answer

Total Members = 40 
Total Males = 75% of 40 = 30 
Total Engineers = Total male Engineers = 50% of males = 15
Total Females = 10

probability that at least one of them is a male or an engineer = Probability that at least one of them is a male = MM + MF 
= 30C2/40C2 + 30C1*10C1/40C2
= (30*29/2)/(40*39/2) + 30*10/(40*39/2)
= 435/780 + 300/780 
= 735/780 
= 147/156

Answer E

kiranteja93 · Answer

Hi Payal,
Thanks for the response.The learning here is subtle : Atleast one case is different from either case which only dances around in the two circles without including neither area as part of possibilities...Interesting.Thankyou

Zynxu · Answer

why is the probability of selecting two women equal to P(selecting two women) = 10C2 / 40C2= 9/156 and not 1/4*1/4 = 1/16 ?

kylebecker9 · Answer

They are not independent events. You can calculate your way but after you have already selected one woman, you then have 9 left out of the remaining 39 people.

1/4 * 9/39 = 9/156

PreiteeRanjan · Answer

50% of them are  the only engineers  in the club.
mark the word and the problem is solved.
p atleat(men or engineer)=1-(female)/total sample space
10c2/40c2 is the answer 
 E

exc4libur · Answer

Club…M…………F……total
eng….15…………0……15
not…..15…………10……25
total…3/4*40…1/4*40…40

1-p(w and w)=1-(10/40*9/39)=1-(3/52)=49/52=147/156

Ans (E)

rmahe11 · Answer

I feel the problem here is wording of the question when it says "50 percent of them" shouldnt it be 50 percent of overall members in the club are engineers and not 50 percent of men.

Kinshook · Answer

Given: In a club, 75% of the members are men, and 50% of them are the only engineers in the club. If total number of members in the club is 40 and two of them are selected at random.

Asked:  Then what is the probability that at least one of them is a male or an engineer?

Men  Women  Total  
  Engineer  15=50%*30  0  15  
  ~Engineer  30-15=15   25-15=10 40-15=25  
  Total  30=75%  10=25%  40=100%

The probability that at least one of them is a male or an engineer
= 1 - Probabilty that none is a male or an engineer 
= 1 - Probabilty that all of the two are women
= 1 - 10C2/40C2
= 1 - 9/156
= 147/156

​​​​​​​IMO E

bumpbot · Answer

Automated notice from GMAT Club BumpBot:

A member just gave Kudos to this thread, showing it’s still useful. I’ve bumped it to the top so more people can benefit. Feel free to add your own questions or solutions.

This post was generated automatically.

In a club, 75% of the members are men, and 50% of them are the only...

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

	Men	Women	Total
Engineer	15=50%*30	0	15
~Engineer	30-15=15		40-15=25
Total	30=75%	10=25%	40=100%

GMAT Problem Solving (PS) Questions

In a club, 75% of the members are men, and 50% of them are the only...

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