In an office that employs 120 people, m% of the employees

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In an office that employs 120 people, m% of the employees are male, and c% of the employees are members of the custodial staff. How many employees are females who are not members of the custodial staff?

(1) m + c = 50
(2) The number of female employees who are members of the custodial staff is four.

OA E

Source: Veritas Prep
Source: — Data Sufficiency |

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by Jay@ManhattanReview » Sat Sep 22, 2018 12:18 am

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BTGmoderatorDC wrote:In an office that employs 120 people, m% of the employees are male, and c% of the employees are members of the custodial staff. How many employees are females who are not members of the custodial staff?

(1) m + c = 50
(2) The number of female employees who are members of the custodial staff is four.

OA E

Source: Veritas Prep
Given:

1. Total number of employees = 120
2. Total number of male employees = 120*m/100 = 6m/5
3. Thus, total number of female employees = 120 - 6m/5
4. Total number of custodial staff = 120*c/100 = 6c/5
5. Thus, total number of non-custodial staff = 120 - 6c/5

We have to determine the total number of non-custodial female staff.

See the solution in the image.

Image

The correct answer: E

Hope this helps!

-Jay
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by GMATGuruNY » Sat Sep 22, 2018 2:22 am

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BTGmoderatorDC wrote:In an office that employs 120 people, m% of the employees are male, and c% of the employees are members of the custodial staff. How many employees are females who are not members of the custodial staff?

(1) m + c = 50
(2) The number of female employees who are members of the custodial staff is four.
Use a DOUBLE-MATRIX to organize the data.

Statements combined:
Case 1: m=25% and c=25%
Total number of males = (25/100)(120) = 30.
Total number of custodial employees = (25/100)(120) = 30.
The following matrix is yielded:
Image
In this case, the number of noncustodial female employees = 86.

Case 2: m=30% and c=20%
Total number of males = (30/100)(120) = 36.
Total number of custodial employees = (20/100)(120) = 24.
The following matrix is yielded:
Image
In this case, the number of noncustodial female employees = 80.

Since the number of noncustodial female employees can be different values,
the two statements combined are INSUFFICIENT.

The correct answer is E.
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I thought I'd point out that the two approaches above are known as 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.
Here, we have a population of students, and the two characteristics are:
- male or female
- custodial staff or not custodial staff

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: https://www.gmatprepnow.com/module/gmat- ... ems?id=919

Once you're familiar with this technique, you can attempt these additional practice questions:

Easy Problem Solving questions
- https://www.beatthegmat.com/finance-maj ... 67425.html

Medium Problem Solving questions
- https://www.gmatprepnow.com/module/gmat- ... /video/920
- https://www.beatthegmat.com/posted-spee ... 72374.html
- https://www.beatthegmat.com/motel-t271938.html
- https://www.beatthegmat.com/of-the-appl ... 70255.html
- https://www.beatthegmat.com/opening-nig ... 64869.html
- https://www.beatthegmat.com/at-least-10 ... 74669.html
- https://www.beatthegmat.com/prblem-solving-t279424.html

Difficult Problem Solving questions
- https://www.gmatprepnow.com/module/gmat- ... /video/946
- https://www.beatthegmat.com/ratio-problem-t268339.html
- https://www.beatthegmat.com/overlapping ... 65223.html
- https://www.beatthegmat.com/fractions-t264254.html
- https://www.beatthegmat.com/overlapping ... 64092.html
- https://www.beatthegmat.com/mba/2011/05 ... question-2

Easy Data Sufficiency questions
- https://www.gmatprepnow.com/module/gmat- ... /video/943
- https://www.beatthegmat.com/for-what-pe ... 70596.html
- https://www.beatthegmat.com/ds-quest-t187706.html

Medium Data Sufficiency questions
- https://www.beatthegmat.com/sets-matrix-ds-t271914.html
- https://www.beatthegmat.com/each-of-peo ... 71375.html
- https://www.beatthegmat.com/a-manufacturer-t270331.html
- https://www.beatthegmat.com/in-costume- ... 69355.html
- https://www.beatthegmat.com/mba/2011/05 ... question-1

Difficult Data Sufficiency questions
- https://youtu.be/dsCeqF9Kbk8
- https://www.beatthegmat.com/double-set- ... 71423.html
- https://youtu.be/dOZ9KM1m5Hs
- https://www.beatthegmat.com/sets-t269449.html
- https://www.beatthegmat.com/mba/2011/05 ... question-3

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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