Last visit was: 19 Nov 2025, 09:09 It is currently 19 Nov 2025, 09:09
Close
GMAT Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Close
Request Expert Reply
Confirm Cancel
User avatar
sunland
Joined: 07 Jun 2010
Last visit: 23 Jul 2010
Posts: 12
Own Kudos:
184
 [52]
Given Kudos: 6
Location: mumbai
Concentration: finance
Schools:isb
Posts: 12
Kudos: 184
 [52]
3
Kudos
Add Kudos
49
Bookmarks
Bookmark this Post
Most Helpful Reply
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 19 Nov 2025
Posts: 105,389
Own Kudos:
Given Kudos: 99,977
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 105,389
Kudos: 778,283
 [18]
5
Kudos
Add Kudos
13
Bookmarks
Bookmark this Post
User avatar
DavidArchuleta
Joined: 05 Jul 2008
Last visit: 12 Nov 2013
Posts: 74
Own Kudos:
271
 [10]
Given Kudos: 40
GMAT 1: 740 Q51 V38
GMAT 1: 740 Q51 V38
Posts: 74
Kudos: 271
 [10]
6
Kudos
Add Kudos
4
Bookmarks
Bookmark this Post
General Discussion
avatar
Detran
Joined: 21 Apr 2010
Last visit: 26 Mar 2015
Posts: 17
Own Kudos:
98
 [4]
GMAT 1: 710 Q48 V40
GMAT 1: 710 Q48 V40
Posts: 17
Kudos: 98
 [4]
2
Kudos
Add Kudos
2
Bookmarks
Bookmark this Post
sunland
19. Committee X and Committee Y , which have no
common members, will combine to form Committee
Z . Does Committee X have more members than
Committee Y ?

(1) The average (arithmetic mean) age of the
members of Committee X is 25.7 years and the
average age of the members of Committee Y is
29.3 years.

(2) The average (arithmetic mean) age of the
members of Committee Z will be 26.6 years.

1 Statement 1 is insufficient. Knowing the average of the groups gives us no idea about how many members there are

2. Statement 2 is insufficient because knowing the average of the group does not tell you anything about the number in the group


Together they are suff because the info together can tell you the relative portion of the two groups.


A(25.7) + B(29.3) / A+B = 26.6 is a weighted average problem. It can tell you the relative size of one group to the other.

You can also think of the problem another way. Since the avg age of the groups is closer to community X. You know there must be more people in X.
avatar
Shko1
Joined: 21 Aug 2011
Last visit: 12 Jul 2012
Posts: 22
Own Kudos:
Concentration: Leadership, Finance
GMAT Date: 04-02-2012
GPA: 3.79
WE:Corporate Finance (Finance: Investment Banking)
Products:
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Question: Couldn't both committees have the same number of members but one committee just have older members?
avatar
Detran
Joined: 21 Apr 2010
Last visit: 26 Mar 2015
Posts: 17
Own Kudos:
GMAT 1: 710 Q48 V40
GMAT 1: 710 Q48 V40
Posts: 17
Kudos: 98
Kudos
Add Kudos
Bookmarks
Bookmark this Post
If that were true u would expect mean age of z to b
the arithmatic mean, which would be directly betw
een x and y
. The weighs would be equal for each group in that case

Posted from my mobile device [img]
https://gmatclub.com/static/mobile.png[/img]
User avatar
AbeinOhio
Joined: 22 Feb 2012
Last visit: 02 Nov 2016
Posts: 74
Own Kudos:
75
 [4]
Given Kudos: 25
Schools: HBS '16
GMAT 1: 670 Q42 V40
GMAT 2: 740 Q49 V42
GPA: 3.47
WE:Corporate Finance (Aerospace and Defense)
Schools: HBS '16
GMAT 2: 740 Q49 V42
Posts: 74
Kudos: 75
 [4]
3
Kudos
Add Kudos
1
Bookmarks
Bookmark this Post
I had to think about this a few times :(


I forgot to rephrase the question and thats what got me in the end..

Basically the question is asking what is # of X members/# of Y Members

1) Ins
2) Ins

1 + 2 ) Ins to solve for X and Y but

based on X as number of comm x members and Y as number of comm y members...

you can say:

(25.7 * x + 29.3 (y)) / (x + y) = 26.6

then you can say that 25.7 x + 29.3 y = 26.6x + 26.6y

thus .9x = 2.7y

or x/y = 1/3

I kept banging my head against a wall thinking i cant solve for x or y with one equation..
User avatar
Maverick04308
Joined: 25 Sep 2012
Last visit: 05 Oct 2018
Posts: 7
Own Kudos:
Given Kudos: 13
Concentration: General Management
Posts: 7
Kudos: 33
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
There is actually no need for some variables and formulas here.

Committee X and Committee Y , which have no common members, will combine to form Committee Z . Does Committee X have more members than Committee Y ?

(1) The average (arithmetic mean) age of the members of Committee X is 25.7 years and the average age of the members of Committee Y is 29.3 years. Insufficient on its own.

(2) The average (arithmetic mean) age of the members of Committee Z will be 26.6 years. Insufficient on its own.

(1)+(2) The difference between the averages of Z and X is 26.6-25.7=0.9 and the difference between the averages of Z and Y is 29.3-26.6=2.7. Since the average of Z is closer to the average of X then X must have more members than Y (to draw the overall average closer to its own average). Sufficient.

Notice that we cannot find # of members in X or Y, though based on the difference in averages (0.9 and 2.7) we can deduce that the ration of members in X and Y is 3:1.

Answer: C.


I agree with this explanation Bunuel, however I have one doubt while solving questions using this approach. What if one committee has say 3 members with age 200(avg 200) :( and other has say 10 members with age 10 (avg=10) . In this case the average age of group (266) is closer to the committee with fewer members.
guess there is a problem in my basics...if u could please throw some light on weighted avg
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 19 Nov 2025
Posts: 105,389
Own Kudos:
778,283
 [1]
Given Kudos: 99,977
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 105,389
Kudos: 778,283
 [1]
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Maverick04308
Bunuel
There is actually no need for some variables and formulas here.

Committee X and Committee Y , which have no common members, will combine to form Committee Z . Does Committee X have more members than Committee Y ?

(1) The average (arithmetic mean) age of the members of Committee X is 25.7 years and the average age of the members of Committee Y is 29.3 years. Insufficient on its own.

(2) The average (arithmetic mean) age of the members of Committee Z will be 26.6 years. Insufficient on its own.

(1)+(2) The difference between the averages of Z and X is 26.6-25.7=0.9 and the difference between the averages of Z and Y is 29.3-26.6=2.7. Since the average of Z is closer to the average of X then X must have more members than Y (to draw the overall average closer to its own average). Sufficient.

Notice that we cannot find # of members in X or Y, though based on the difference in averages (0.9 and 2.7) we can deduce that the ration of members in X and Y is 3:1.

Answer: C.


I agree with this explanation Bunuel, however I have one doubt while solving questions using this approach. What if one committee has say 3 members with age 200(avg 200) :( and other has say 10 members with age 10 (avg=10) . In this case the average age of group (266) is closer to the committee with fewer members.
guess there is a problem in my basics...if u could please throw some light on weighted avg

The average age of the of the whole group cannot be more than individual averages of the smaller groups, so 266 just cannot be the average age since it's more than both 200 and 10. Generally the weighted average of 2 individual averages (200 and 10) must lie between these individual averages.

In this case the average age of the whole group of 13 members is (3*200+10*10)/13=~54, which is closer to 10 than to 200.

Hope it's clear.
avatar
krrish
Joined: 04 Mar 2013
Last visit: 03 Feb 2014
Posts: 46
Own Kudos:
15
 [1]
Given Kudos: 6
Location: India
Concentration: General Management, Marketing
GPA: 3.49
WE:Web Development (Computer Software)
Posts: 46
Kudos: 15
 [1]
Kudos
Add Kudos
Bookmarks
Bookmark this Post
sunland
Committee X and Committee Y , which have no common members, will combine to form Committee Z . Does Committee X have more members than Committee Y ?

(1) The average (arithmetic mean) age of the members of Committee X is 25.7 years and the average age of the members of Committee Y is 29.3 years.

(2) The average (arithmetic mean) age of the members of Committee Z will be 26.6 years.



here is my take of the question:

s1: gives u two variable terms which can't be equated to any so its insufficent
s2: gives a single variable term : not sufficient
s1 and s2 together then we get a two viable equation which can be used ot find out the relation between x and y
so c is our picK :)
User avatar
jlgdr
Joined: 06 Sep 2013
Last visit: 24 Jul 2015
Posts: 1,311
Own Kudos:
Given Kudos: 355
Concentration: Finance
Posts: 1,311
Kudos: 2,863
Kudos
Add Kudos
Bookmarks
Bookmark this Post
They totally got me on this one, I thought too the following. "Can't X just have older members?" But it is actually the ratio that matters. Even if X has older member the ratio, that is the weight of each of the components will determine the quantity of members in each of both groups, very tricky question indeed totally fell for it

Cheers!
J :)
avatar
abid1986
Joined: 01 Jan 2013
Last visit: 09 Sep 2016
Posts: 38
Own Kudos:
Given Kudos: 131
Location: India
Posts: 38
Kudos: 142
Kudos
Add Kudos
Bookmarks
Bookmark this Post
sunland
Committee X and Committee Y , which have no common members, will combine to form Committee Z . Does Committee X have more members than Committee Y ?

(1) The average (arithmetic mean) age of the members of Committee X is 25.7 years and the average age of the members of Committee Y is 29.3 years.

(2) The average (arithmetic mean) age of the members of Committee Z will be 26.6 years.


Using Scale Method

25.7----------26.6--------29.3
-X------------Z------------ Y
-------0.3-----:---- 2.7
-------3-------:-----27
-------1--------:----- 9

Therefore
W1/W2 = 9:1
Therefore members in X > Y
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
There is actually no need for variables and formulas here.

Committee X and Committee Y , which have no common members, will combine to form Committee Z . Does Committee X have more members than Committee Y ?

(1) The average (arithmetic mean) age of the members of Committee X is 25.7 years and the average age of the members of Committee Y is 29.3 years. Insufficient on its own.

(2) The average (arithmetic mean) age of the members of Committee Z will be 26.6 years. Insufficient on its own.

(1)+(2) The difference between the averages of Z and X is 26.6-25.7=0.9 and the difference between the averages of Z and Y is 29.3-26.6=2.7. Since the average of Z is closer to the average of X then X must have more members than Y (to draw the overall average closer to its own average). Sufficient.

Notice that we cannot find # of members in X or Y, though based on the difference in averages (0.9 and 2.7) we can deduce that the ratio of members in X and Y is 3:1.

Answer: C.
Bunuel
But, the average of x and y is 27.5 {(25.7+29.3)/2}. May I know why did you deduct 25.7 from the average of z (26.6)?
Thanks__
User avatar
Louis14
Joined: 01 Nov 2019
Last visit: 04 Nov 2023
Posts: 249
Own Kudos:
Given Kudos: 472
GMAT 1: 680 Q48 V34
GPA: 3.56
GMAT 1: 680 Q48 V34
Posts: 249
Kudos: 125
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
There is actually no need for variables and formulas here.

Committee X and Committee Y , which have no common members, will combine to form Committee Z . Does Committee X have more members than Committee Y ?

(1) The average (arithmetic mean) age of the members of Committee X is 25.7 years and the average age of the members of Committee Y is 29.3 years. Insufficient on its own.

(2) The average (arithmetic mean) age of the members of Committee Z will be 26.6 years. Insufficient on its own.

(1)+(2) The difference between the averages of Z and X is 26.6-25.7=0.9 and the difference between the averages of Z and Y is 29.3-26.6=2.7. Since the average of Z is closer to the average of X then X must have more members than Y (to draw the overall average closer to its own average). Sufficient.

Notice that we cannot find # of members in X or Y, though based on the difference in averages (0.9 and 2.7) we can deduce that the ratio of members in X and Y is 3:1.

Answer: C.



Can't they have same number of members?

For example, say X has two members of ages: 20 and 66. (Average= 43)
Similarly, say Y also has two members of ages: 20 and 20. (Average= 20)

Committee Z: 20+66+20+20/4= 32 (Average of Z)

(All of these twenty year olds are three different individuals, as the two set don't share any member.)

Now, as Bunuel did: 43-32=11; 32-20=12. So the two groups, X and Y, would be in the ratio 12:11.

As we can see, if we go by the logic above, then X should have more members than Y as the ratio suggests that. But in reality, X and Y have two members each.

What am I missing?
User avatar
bumpbot
User avatar
Non-Human User
Joined: 09 Sep 2013
Last visit: 04 Jan 2021
Posts: 38,587
Own Kudos:
Posts: 38,587
Kudos: 1,079
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
Moderators:
Math Expert
105389 posts
496 posts