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# QOTD#20 List X: 2, 5, s, t List Y: 2, 5, t The average

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GRE Prep Club Legend
Joined: 07 Jun 2014
Posts: 4809
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
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Kudos [?]: 1975 [0], given: 397

QOTD#20 List X: 2, 5, s, t List Y: 2, 5, t The average [#permalink]  07 Sep 2016, 12:57
Expert's post
00:00

Question Stats:

42% (01:23) correct 57% (01:21) wrong based on 28 sessions
List X: 2, 5, s, t
List Y: 2, 5, t

The average (arithmetic mean) of the numbers in list X is equal to the average of the numbers in list Y.

 Quantity A Quantity B s 0

A) Quantity A is greater.
B) Quantity B is greater.
C) The two quantities are equal.
D) The relationship cannot be determined from the information given

Practice Questions
Question: 6
Page: 177
[Reveal] Spoiler: OA

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Sandy
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GRE Prep Club Legend
Joined: 07 Jun 2014
Posts: 4809
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
Followers: 123

Kudos [?]: 1975 [0], given: 397

Re: QOTD#20 List X: 2, 5, s, t List Y: 2, 5, t The average [#permalink]  07 Sep 2016, 13:01
Expert's post
Explanation

Since you are given that the average of the 4 numbers in list X is equal to the average of the 3 numbers in list Y, it follows that
$$\frac{(2+5+s+t)}{4} = \frac{(2+5+t)}{3}$$. To make it easier to compare Quantity A
and Quantity B, you can simplify this equation as follows.

$$\frac{(2+5+s+t)}{4} = \frac{(2+5+t)}{3}$$
$$\frac{(7+s+t)}{4} = \frac{(7+t)}{3}$$
$$3s=7+t$$

From the equation 3s = 7 + t, if t = –7, then s = 0, but if t = 0, then s > 0. In one case, the quantities are equal, and in the other case, Quantity A is greater. Therefore the correct answer is Choice D.
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Sandy
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Kudos [?]: 1989 [0], given: 20

Re: QOTD#20 List X: 2, 5, s, t List Y: 2, 5, t The average [#permalink]  12 Jun 2019, 07:12
Expert's post
sandy wrote:
List X: 2, 5, s, t
List Y: 2, 5, t

The average (arithmetic mean) of the numbers in list X is equal to the average of the numbers in list Y.

 Quantity A Quantity B s 0

A) Quantity A is greater.
B) Quantity B is greater.
C) The two quantities are equal.
D) The relationship cannot be determined from the information given

Another approach is to test some values.

Let t = -7
This means list Y is 2, 5, -7, so list Y has an average of 0
For list X to have an average of 0, s must = 0
In this case, quantity A and quantity B are equal.

Let t = 2
This means list Y is 2, 5, 2, so list Y has an average of 3
For list X to have an average of 3, s must = 3
In this case, quantity A is greater than quantity B

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Re: QOTD#20 List X: 2, 5, s, t List Y: 2, 5, t The average   [#permalink] 12 Jun 2019, 07:12
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# QOTD#20 List X: 2, 5, s, t List Y: 2, 5, t The average

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