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# Of the 84 parents who attended a meeting at a school, 35

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Of the 84 parents who attended a meeting at a school, 35 [#permalink]

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24 Mar 2011, 22:10
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Difficulty:

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Question Stats:

74% (01:55) correct 26% (02:01) wrong based on 570 sessions

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Of the 84 parents who attended a meeting at a school, 35 volunteered to supervise children during the school picnic and 11 volunteered both to supervise children during the picnic and to bring refreshments to the picnic.If the number of parents who volunteered to bring refreshments was 1.5 times the number of parents who neither volunteered to supervise children during the picnic nor volunteered to bring refreshments, how many of the parents volunteered to bring refreshments?

A) 25
B) 36
C) 38
D) 42
E) 45

Official Guide 12 Question

 Question: 14 Page: 22 Difficulty: 750

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Video Explanations:
[Reveal] Spoiler: OA

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Last edited by GMATD11 on 24 Mar 2011, 23:56, edited 1 time in total.

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Re: is Double Set martix a good option to solve dis question [#permalink]

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24 Mar 2011, 23:04
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GMATD11 wrote:
14) of the 84 parents who attended a meeting at a school, 35 volunteered to supervise children during the school picnic and 11 volunteered both to supervise children during the picnic and to bring refreshments to the picnic.If the number of parents who volunteered to bring refreshments was 1.5 times the number of parents who neither volunteered to supervise children during the picnic nor volunteered to bring refreshments, how many of the parents volunteered to bring refreshments?

a) 25
b) 36
c) 38
d) 42
e) 45

Bring refreshment Volunteered Total
to Supervise 11 35
Volunteered x=? y
Total 11+x 35+y 84

11+x+35+y=84
x+y= 38
x=1.5y
x=24

A

is dis the correct method to solve.

when to use double set matrix and when to use venn diagram for two type of information

Are you sure about the OA? I thinker the right answer should be 36. Here is how:

Total = Supervise + Refreshments + None - Both

We are given Total = 84, Supervise = 35, Both = 11 and Refreshments = 1.5*None

So, we get 84=35+1.5*None+None-11 or None = 24

So, Refreshments = 1.5*24 = 36.

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Re: is Double Set martix a good option to solve dis question [#permalink]

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25 Mar 2011, 19:00
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GMATD11 wrote:
14) of the 84 parents who attended a meeting at a school, 35 volunteered to supervise children during the school picnic and 11 volunteered both to supervise children during the picnic and to bring refreshments to the picnic.If the number of parents who volunteered to bring refreshments was 1.5 times the number of parents who neither volunteered to supervise children during the picnic nor volunteered to bring refreshments, how many of the parents volunteered to bring refreshments?

a) 25
b) 36
c) 38
d) 42
e) 45

when to use double set matrix and when to use venn diagram for two type of information

Most GMAT questions can be easily and quickly solved using Venn Diagrams. (Different people prefer different strategies but I have found that no matter how tricky the question wording is, once you draw the Venn diagram, it all seems very clear)

Check out the Venn diagram for this question:
Attachment:

Ques2.jpg [ 13.38 KiB | Viewed 25248 times ]

Now, since it is given that
x+11 = 1.5 (84-(24+11+x))
x = 25
So number of parents who volunteered to bring refreshments = x+11 = 25+11 = 36
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Re: is Double Set martix a good option to solve dis question [#permalink]

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27 Mar 2011, 00:51
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This can be solved by using Double Matrix too, depends on what you're comfortable with. Please see the attached image.

So 2.5x + 24 = 84

=> 2.5x = 60

=> x = 600/25 = 24

=> 1.5x = 36

Attachments

Parents_Meeting.png [ 10.27 KiB | Viewed 25002 times ]

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Re: is Double Set martix a good option to solve dis question [#permalink]

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27 Mar 2011, 01:08
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Btw, this can be done without either as :

y = number of parents who volunteered to bring refreshments only

x = the number of parents who neither volunteered to supervise children during the picnic nor volunteered to bring refreshments

So 11 + y = 1.5x

and 84 - x = 11 + y + (35 - 11)

=> 84 - x = 1.5x + 24

=> 2.5x = 60

=> x = 24 and 1.5x = 36
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Re: is Double Set martix a good option to solve dis question [#permalink]

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27 Mar 2011, 11:36
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For me, the easiest way to solve questions similar to this one is by the formula

T=A+B-AB+NON
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Re: is Double Set martix a good option to solve dis question [#permalink]

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29 Mar 2011, 03:50
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The Double Set Matrix draws the equation for you nicely. Yes! But, if you can solve it without the help of this tool.. Good for you..

The answer is 1.5 x 24 = 36!!
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answer.png [ 3.06 KiB | Viewed 24906 times ]

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Re: is Double Set martix a good option to solve dis question [#permalink]

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13 Jun 2011, 07:56
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neither volunteered to supervise children during the picnic nor volunteered to bring refreshments = x
number of parents volunteered to bring refreshments = 1.5x
so, 84 = 35 + 1.5x - 11 + x
2.5x = 60
x = 24
Thus, number of parents volunteered to bring refreshments = 24*1.5=36
Ans. B
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Re: Of the 84 parents who attended a meeting at a school, 35 [#permalink]

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25 Feb 2012, 22:13
Baten80 wrote:
neither volunteered to supervise children during the picnic nor volunteered to bring refreshments = x
number of parents volunteered to bring refreshments = 1.5x
so, 84 = 35 + 1.5x - 11 + x
2.5x = 60
x = 24
Thus, number of parents volunteered to bring refreshments = 24*1.5=36
Ans. B
Why isn't the overlap substracted also from the parents who bring refreshments?

When we are given 35 who volunteered to supervise, we substract the overlap (11), so total = 24; why isn't the final number of parents who voluntereed to refreshments = 1.5x - 11 ?

84 = (35-11) + (1.5x - 11) + x

???

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Re: Of the 84 parents who attended a meeting at a school, 35 [#permalink]

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26 Feb 2012, 01:48
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ElDiablo wrote:
Baten80 wrote:
Of the 84 parents who attended a meeting at a school, 35 volunteered to supervise children during the school picnic and 11 volunteered both to supervise children during the picnic and to bring refreshments to the picnic.If the number of parents who volunteered to bring refreshments was 1.5 times the number of parents who neither volunteered to supervise children during the picnic nor volunteered to bring refreshments, how many of the parents volunteered to bring refreshments?
A) 25
B) 36
C) 38
D) 42
E) 45

neither volunteered to supervise children during the picnic nor volunteered to bring refreshments = x
number of parents volunteered to bring refreshments = 1.5x
so, 84 = 35 + 1.5x - 11 + x
2.5x = 60
x = 24
Thus, number of parents volunteered to bring refreshments = 24*1.5=36
Ans. B
Why isn't the overlap substracted also from the parents who bring refreshments?

When we are given 35 who volunteered to supervise, we substract the overlap (11), so total = 24; why isn't the final number of parents who voluntereed to refreshments = 1.5x - 11 ?

84 = (35-11) + (1.5x - 11) + x

???

Because parents who supervise (1.5x) consist of the parent who supervise AND bring refreshments (11) and of the parents who supervise but DO NOT bring refreshments (1.5x-11). So if we subtract 11 (the parent who supervise AND bring refreshments) we'll get the parents who supervise but DO NOT bring refreshments and no the total parents who supervise.

Generally: {Total}={Supervise}+{Refreshments}-{Both}+{Neither} (notice that we subtract {Both} since it's already included twice: once in {Supervise} and once in {Refreshments});

Given: 84=35+1.5x-11+x --> x=24 --> 1.5x=36.

Below matrix might help to understand the question better:
Attachment:

Parents.PNG [ 5.62 KiB | Viewed 23989 times ]
Notice that numbers in black are given and in red are calculated. We need the value of yellow box: 1.5x+(24+x)=84 --> x=24 --> 1.5x=36.

Hope it's clear.
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Re: Of the 84 parents who attended a meeting at a school, 35 [#permalink]

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01 Dec 2012, 23:48
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You can use a chart to help you solve this problem as taught in the MGMAT.

= S stands for Supervise and ~S means not Supervise
= R stands for Bring Refreshments and ~R means not Bring Refreshments

So how to use the chart?
= Place in the rightmost corner the total of parents which is 84.
= We know that there are 35 who volunteered to Supervise but since we do not know whether they are R or ~R, we put 35 at the bottom of column S.
= We know that there are 11 who are both S and R. So we placed 11 accordingly.
= We know those who are R is 1.5 times of those who are ~R and ~S. So we use a variable x to denote that relationship.

From the chart we can construct our equation clearly.

24 + x + 1.5X = 84

Solve for X.
X = 24

We know R = 1.5X = 1.5(24) = 36

Attachments

c.jpg [ 5.94 KiB | Viewed 22277 times ]

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Re: Of the 84 parents who attended a meeting at a school, 35 [#permalink]

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20 Mar 2013, 05:16
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The language used in these problems confuses me!!
Example : 35 volunteered to supervise children during the school picnic ---> Only supervise + supervise & bring refreshments
However, how many of the parents volunteered to bring refreshments --> This ideally should mean: supervise & bring refreshments + Only bring refreshment.
But sadly the answer choice has value which = only bring refreshment
Any suggestions on how to go about?
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Re: Of the 84 parents who attended a meeting at a school, 35 [#permalink]

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20 Mar 2013, 05:20
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summer101 wrote:
The language used in these problems confuses me!!
Example : 35 volunteered to supervise children during the school picnic ---> Only supervise + supervise & bring refreshments
However, how many of the parents volunteered to bring refreshments --> This ideally should mean: supervise & bring refreshments + Only bring refreshment.
But sadly the answer choice has value which = only bring refreshment
Any suggestions on how to go about?

Not so, check here: of-the-84-parents-who-attended-a-meeting-at-a-school-35-volunteered-111450.html#p1050015
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Re: Of the 84 parents who attended a meeting at a school, 35 [#permalink]

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20 Mar 2013, 06:46
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Expert's post
summer101 wrote:
The language used in these problems confuses me!!
Example : 35 volunteered to supervise children during the school picnic ---> Only supervise + supervise & bring refreshments
However, how many of the parents volunteered to bring refreshments --> This ideally should mean: supervise & bring refreshments + Only bring refreshment.
But sadly the answer choice has value which = only bring refreshment
Any suggestions on how to go about?

You need to actively look for the word 'only' in these questions.

35 volunteered to supervise children: Overall, 35 people volunteered to supervise. This includes people who volunteered to do both - supervise and bring refreshments

35 volunteered to only supervise children: Does not include people who volunteered to do both.

How many of the parents volunteered to bring refreshments? Overall, how many volunteered to bring refreshments - it will include people who volunteered to do both. There is no ambiguity here.

How many of the parents volunteered to only bring refreshments? Now this is only refreshments.

Re-consider the calculations done above.
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Re: Of the 84 parents who attended a meeting at a school, 35 [#permalink]

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23 Mar 2013, 11:49
The difficulty for this question is 750. Impossible! Then some of the questions I came across in the OG are at a 10,000 difficulty

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Re: Of the 84 parents who attended a meeting at a school, 35 [#permalink]

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20 Oct 2014, 19:44
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Re: Of the 84 parents who attended a meeting at a school, 35 [#permalink]

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18 Jul 2015, 03:01
Hi,

I tried solving this problem exactly as per the method described.

Solving the equation that you have mentioned:
x+11 = 1.5 (84-(24+11+x))
x +11 = 1.5 (84-24-11-x)
x + 11 = 1.5 (49 - x)
Solving for x gives x=29.4

VeritasPrepKarishma wrote:
GMATD11 wrote:
14) of the 84 parents who attended a meeting at a school, 35 volunteered to supervise children during the school picnic and 11 volunteered both to supervise children during the picnic and to bring refreshments to the picnic.If the number of parents who volunteered to bring refreshments was 1.5 times the number of parents who neither volunteered to supervise children during the picnic nor volunteered to bring refreshments, how many of the parents volunteered to bring refreshments?

a) 25
b) 36
c) 38
d) 42
e) 45

when to use double set matrix and when to use venn diagram for two type of information

Most GMAT questions can be easily and quickly solved using Venn Diagrams. (Different people prefer different strategies but I have found that no matter how tricky the question wording is, once you draw the Venn diagram, it all seems very clear)

Check out the Venn diagram for this question:
Attachment:
Ques2.jpg

Now, since it is given that
x+11 = 1.5 (84-(24+11+x))
x = 25
So number of parents who volunteered to bring refreshments = x+11 = 25+11 = 36

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Re: Of the 84 parents who attended a meeting at a school, 35 [#permalink]

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08 Dec 2015, 11:53
GMATD11 wrote:
Of the 84 parents who attended a meeting at a school, 35 volunteered to supervise children during the school picnic and 11 volunteered both to supervise children during the picnic and to bring refreshments to the picnic.If the number of parents who volunteered to bring refreshments was 1.5 times the number of parents who neither volunteered to supervise children during the picnic nor volunteered to bring refreshments, how many of the parents volunteered to bring refreshments?

A) 25
B) 36
C) 38
D) 42
E) 45

Official Guide 12 Question

 Question: 14 Page: 22 Difficulty: 750

Find All Official Guide Questions

Video Explanations:

Again, unless ONLY is mentioned DO NOT ASSUME that 35 does not include 11 who volunteered to do both (supervise as well as bring refreshments). CRITICAL for such question types.
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Re: Of the 84 parents who attended a meeting at a school, 35 [#permalink]

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23 Dec 2016, 21:56
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Re: Of the 84 parents who attended a meeting at a school, 35   [#permalink] 23 Dec 2016, 21:56
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