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Within a group of students, x students are taking English, y [#permalink]
21 Jun 2018, 06:29

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Question Stats:

61% (01:16) correct
38% (00:41) wrong based on 36 sessions

Within a group of students, x students are taking English, y students are taking Math, and z students are taking both English and Math. Which of the following represents the number of students who are taking English or Math but not both?

A) x + y - z B) x + y + z C) 2x + 2y - z D) x + y - 2z E) x + y + 2z

Brent Hanneson – Creator of greenlighttestprep.com If you enjoy my solutions, you'll like my GRE prep course. Sign up for GRE Question of the Dayemails

Re: Within a group of students, x students are taking English, y [#permalink]
22 Jun 2018, 08:00

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GreenlightTestPrep wrote:

Within a group of students, x students are taking English, y students are taking Math, and z students are taking both English and Math. Which of the following represents the number of students who are taking English or Math but not both?

Here E = number of students taking English Y= number of students taking Math Z= number of students taking both English and Math

Therefore number of students taking only english = X-Z

and number of student taking only math = Y-Z

Hence number of students who are taking English or Math but not both = (X-Z)+(Y-Z) = X+Y-2Z
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Re: Within a group of students, x students are taking English, y [#permalink]
24 Jun 2018, 06:16

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Expert's post

GreenlightTestPrep wrote:

Within a group of students, x students are taking English, y students are taking Math, and z students are taking both English and Math. Which of the following represents the number of students who are taking English or Math but not both?

A) x + y - z B) x + y + z C) 2x + 2y - z D) x + y - 2z E) x + y + 2z

We can solve this by using 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 students, and the two characteristics are: - taking English or not taking English - taking Math or not taking Math

We want to find: (number of students taking English but not Math) + (number of students taking Math but not English) So, we can set up our matrix as follows:

We need to find the number of students in the 2 boxes with stars in them.

GIVEN: x students are taking English, and y students are taking Math So, we can add this information to our diagram as follows:

GIVEN: z students are taking both English and Math So, we can add this information to our diagram as follows:

Let's first examine the top ROW. If a total of x students are taking English, and z of them are also taking Math, then x-z of them are NOT taking Math.

Now examine the left-hand COLUMN. If a total of y students are taking Math, and z of them are also taking English, then y-z of them are NOT taking English.

So, the number of students who are taking English or Math but not both = (x - z) + (y - z) = x + y - 2z

Answer: D

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