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What is the average (arithmetic mean) of the first 90 measurements

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What is the average (arithmetic mean) of the first 90 measurements  [#permalink]

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New post 23 Jun 2015, 21:09
2
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A
B
C
D
E

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Question Stats:

92% (00:58) correct 8% (00:49) wrong based on 237 sessions

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What is the average (arithmetic mean) of the first 90 measurements in a certain list of 92 measurements?

    (1) The average of 92 measurements is 7.0 centimeters.

    (2) The average of the last 2 measurements is 7.2 centimeters.
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Re: What is the average (arithmetic mean) of the first 90 measurements  [#permalink]

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New post 23 Jun 2015, 21:26
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mimi0102 wrote:
What is the average (arithmetic mean) of the first 90 measurements in a certain list of 92 measurements?

    (1) The average of 92 measurements is 7.0 centimeters.

    (2) The average of the last 2 measurements is 7.2 centimeters.


You need the average of first 90 measurements.

(1) The average of 92 measurements is 7.0 centimeters.

We don't know what the last two measurements are so we cannot find the average of 90 measurements.

(2) The average of the last 2 measurements is 7.2 centimeters.
We don't know what the first 90 measurements are so we cannot find their average

Together we know that the average of all 92 measurements is 7 so sum of all measurements s 7*92.
We know that the average of last 2 is 7.2 so sum of last two is 7.2*2.

So we get the sum of first 90 measurements = 7*92 - 7.2*2
We can calculate this and divide by 90 to get the average. So both statements together are sufficient.

Answer (C)
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Re: What is the average (arithmetic mean) of the first 90 measurements  [#permalink]

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New post 24 Jun 2015, 04:31
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mimi0102 wrote:
What is the average (arithmetic mean) of the first 90 measurements in a certain list of 92 measurements?

    (1) The average of 92 measurements is 7.0 centimeters.

    (2) The average of the last 2 measurements is 7.2 centimeters.


Statement 1: The average of 92 measurements is 7.0 centimeters

To know the average of 90 measurements that the question is talking about we need to know the sum / average of those two measurements which need to be avoided alongwith the given information.

But no information of those measurements two measurements so far

Hence, NOT SUFFICIENT

Statement 2: The average of the last 2 measurements is 7.2 centimeters.

To know the average of 90 measurements that the question is talking about we need to know the sum / average of those two measurements which need to be avoided. alongwith the information of sum of all the 92 measurements

But no information of those 90 remaining measurements so far

Hence, NOT SUFFICIENT

Combining the two statements

Sum of 92 measurements = 92*7 [from statement 1]
Sum of Last 2 measurements = 7.2*2 [from statement 2]

Hence, Sum of First 90 Measurements = 92*7 - 7.2*2
Hence, SUFFICIENT

Answer: Option
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Re: What is the average (arithmetic mean) of the first 90 measurements  [#permalink]

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New post 21 Dec 2016, 20:00
Nice Official Question.
Here is what i did in this one =>

Let the set be ->
x1
x2
.
.

.
x92


Now Required mean = x1+x2+...x90/90


Statement 1=>
x1+x2+...x90+x91+x92=7*92
No clue of x91 and x92
Hence not sufficient

Statement 2=>
x91+x92=7.2*2
No clue of x1+x2+..x90
Not sufficient

Combing the two statements =>
x1+x2+...x90=7*92-7.2*2

Hence we have the sum => we can get the average

Hence sufficient

Hence C

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Re: What is the average (arithmetic mean) of the first 90 measurements  [#permalink]

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New post 02 Jul 2018, 01:13
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Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: What is the average (arithmetic mean) of the first 90 measurements &nbs [#permalink] 02 Jul 2018, 01:13
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