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

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

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New post 31 May 2015, 15:18
2
Given:

{Total} = {Supervise} + {Refreshments} - {Both} + {Neither}

Given:

{Refreshments} = 1.5 {Neither}

Calculations:

84 = 35 + 1.5 {Neither} - 11 + {Neither}

84 + 11 - 35 = 2.5 {Neither}

60 = 2.5 {Neither}

{Neither} = 24

{Refreshments} = 1.5 {Neither} = 1.5 {24} = 36
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Of the 84 parents who attended a meeting at a school, 35  [#permalink]

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New post 02 Jun 2015, 09:26
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?

Let's say that a = supervise group, b = supervise and refreshment group c = neither
a + b + c = 84
b = ?

a is 35 - 11 = 24 (We subtract so as not to double count those who volunteered for both)
24 + b + c = 84 => b + c = 60
=> c = 60 - b

We're told that b = 1.5c. You can substitute for c.
b = 1.5 (60-b) => 90 - 1.5b
2.5b = 90
b = 36

A) 25
B) 36
C) 38
D) 42
E) 45
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Re: Of the 84 parents who attended a meeting at a school, 35  [#permalink]

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New post 20 Dec 2015, 10:30
danepenell wrote:
This question is confusing me so if anyone could explain in detail I would really appreciate it. I don't understand why it isn't solved the same way as practice question 6... in that question you had Brand A + Brand B + both brands + neither brands = 200 and the answer was 15... on this question though, it is leaving out AND part (11) out of the results. Why isn't it 24 + 1.5x + 11 + × = 84?!?!



I find it easier to write the given info in the following manner:

N (Neither) -parents who will not be supervising or bringing refreshments
S (Supervising) - parents who will be only supervising
R (Refreshments) - parents who will bring refreshments only
R=1.5N

Step 1.
We know that total number of parents is 84, which is N+S+R, to find N ==>
N= 84-S-R, where S = 35-11=24
N=84-24-R
N=60-R, we already know that R=1.5N, substitute to get ==>
N=60-1.5N
2.5N=60
N=24 (24 parents will not be supervising or bringing refreshments)

Step 2.
R=1.5N, substitute to get==>
R=1.5*24
R=36 (parents will bring refreshments!!!)
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Of the 84 parents who attended a meeting at a school, 35  [#permalink]

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New post 18 Feb 2016, 00:47
This question's difficulty level would have jumped an extra 50 points if it had 24 as an answer choice. :)
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Re: Of the 84 parents who attended a meeting at a school, 35  [#permalink]

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New post 12 Sep 2016, 13:09
A = Supervising Children only
B = Both
C = Bring refreshments only
X = Neither

A + B = 35
B = 11
A = 24
B + C = 1.5X
A +B + C + x = 84 (total)

24 + 1.5x + x = 84
2.5x = 60
x = 24
1.5x = 36

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

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New post 06 Oct 2017, 10:57
Bunuel 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


We can use the following formula:

Total = Picnic + Refreshment - Both + Neither

We are given that Total = 84, Picnic = 35, Both = 11, and Refreshment = 1.5 x Neither. Thus, if we let n = Neither, we have:

84 = 35 + 1.5n - 11 + n

84 = 24 + 2.5n

60 = 2.5n

n = 60/2.5 = 600/25 = 24

Since Refreshment = 1.5 x Neither, Refreshment = 1.5 x 24 = 36.

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

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New post 09 Aug 2018, 07:24
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Bunuel 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

Diagnostic Test
Question: 14
Page: 22
Difficulty: 650


Another approach is to use the Double Matrix Method. This technique can be used for most questions featuring a population in which each member has two characteristics associated with it (aka overlapping sets questions).
Here, we have a population of baseball players, and the two characteristics are:
- supervised children or did not supervise children
- bring refreshments or didn't bring refreshments

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.
So, we get the following:
Image

The number of parents who volunteered to bring refreshments was 1.5 times the number of parents who neither volunteered to supervise children during picnic nor volunteered to bring refreshments
If we let x = the number of parents who neither supervised not brought refreshments, then
1.5x = the number of parents who brought refreshments
Image


How many of the parents volunteered to bring refreshments?
In other words, what is the value of 1.5x?
Notice that, if we add the two boxes in the right-hand column, then we see that 24+x = the total number of parents who DIDN'T bring refreshments.
Image

At this point, we know that 1.5x = the number of parents who brought refreshments, and 24+x = the number of parents who DIDN'T bring refreshments.
We can write: 1.5x + (24 + x) = 84 (the total number of parents)
Simplify: 2.5x + 24 = 84
2.5x = 60
x = 24

We already know that 1.5x = the number of parents who brought refreshments
1.5(24) = 36
So, 36 parents brought refreshments

Answer: B

This question type is VERY COMMON on the GMAT, so be sure to master the technique.

To learn more about the Double Matrix Method, watch this video:



One practice question:

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

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New post 09 Aug 2018, 07:30
Total - neither = Supervise + Refreshment - Both
Total = 84
Neither = N
Supervise = 35
Refreshment = 1.5N
Both = 11

84-N = 35+1.5N-11
2.5N = 60
N=24

Refreshment = 24*1.5 = 36
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Re: Of the 84 parents who attended a meeting at a school, 35  [#permalink]

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New post 09 Aug 2018, 23:29
As with many GMAT questions, there are many ways to arrive at the answer to this question! I am adding my two cents as part of my new project to go through all of the Quant questions in the 2019 Official Guide and share my suggested "GMAT Timing Tips" for each one: that is, what could you notice or do to be able to answer each question more efficiently? For this question, my GMAT Timing Tips are:

    Two-set Venn Diagrams: Draw out the Venn Diagram to quickly see how the numbers you are given relate to what you are asked to calculate. As many people have done on this thread, you can find that 24 parents volunteered only to supervise children.
    Use smart variables to represent unknowns: I recommend using the variable R to represent the total number of parents who volunteered to bring refreshments, because that is what the question asks us to solve for. Then, using the Venn Diagram and the information in the question, write the equation R = 1.5(84 - 24 - R), and just solve for R.

I'm also planning to create video solutions demonstrating how to use my GMAT Timing Tips for each of the Official Guide Quant questions. This will take a while, but I'll start with the those that I get requests for first. If you would me to create a video solution for this question, please go to the page that I have created for this question and vote for or share it: Of the 84 parents who attended a meeting at a school, 35..

You can also ask me to answer a question about this GMAT practice question by asking it in this thread, or by using the question form on the page above, and I'll address it in my video solution. Please let me know if you have any questions!
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Re: Of the 84 parents who attended a meeting at a school, 35  [#permalink]

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New post 15 Oct 2018, 16:08
Bunuel 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

Diagnostic Test
Question: 14
Page: 22
Difficulty: 650

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

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New post 08 Dec 2018, 14:35
Hi everyone,

I understand the math behind this question, however I am struggling with one particular part of the problem. In the opening statement, "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." What part clues you into the fact that you need to subtract the intersection of the set of parents that supervised and the set that supervised and brought refreshments?

How do I know that the 11 parents are certainly the intersection of the parents who brought drinks and the parents who supervised? How would I know that we are not dealing with three independent sets?
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Of the 84 parents who attended a meeting at a school, 35  [#permalink]

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New post 25 Jun 2019, 10:01
I'm sorry for the stupid questions but anyway:

1.
Quote:
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

Why it's not 1.5 * (84-35)

2.
Quote:
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.


In official guide solution: 35-11?
But I read it like 35 and 11 but not 11 among 35
What's the trick?
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Of the 84 parents who attended a meeting at a school, 35   [#permalink] 25 Jun 2019, 10:01

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