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Is the average (arithmetic mean) of a and b less than 40?

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Is the average (arithmetic mean) of a and b less than 40? [#permalink]

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Is the average (arithmetic mean) of a and b less than 40?

(1) The average (arithmetic mean) of 3a and 3b is 117.
(2) b = 5a

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[Reveal] Spoiler: OA

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Is the average (arithmetic mean) of a and b less than 40? [#permalink]

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New post 02 Oct 2015, 01:35
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It has to be A

(3a+3b)/2=117
(a+b)/2=39

so first statement is sufficient.

from b
6a/2=3a now a can be anything from 1 to 100

so insufficient

+1Kudos if you like solution :-D
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Re: Is the average (arithmetic mean) of a and b less than 40? [#permalink]

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New post 06 Oct 2015, 08:11
Bunuel wrote:
Is the average (arithmetic mean) of a and b less than 40?

(1) The average (arithmetic mean) of 3a and 3b is 117.
(2) b = 5a

Kudos for a correct solution.


VERITAS PREP OFFICIAL SOLUTION:

Question Type: Yes/No. “is the average of a and b less than 40?”

Given information from the question stem: You’re dealing with averages. One helpful tool to use when asked about the average of a group of numbers is to use the formula “Average * number = total.” In this case if the average is 40 and there are two numbers (a and b), then the question is really asking is (A+B)/2 < 40 or is “A +B < 80.”

Statement 1: if the average of 3a and 3b is 117 this means that “3a + 3b = 234.” If you divide by sides by 3 then you get “a + b = 78.” This is sufficient to answer the question. “Yes, the average of a + b < 40.” This statement is sufficient. The correct answer is either A or D.

Note: It would not be necessary to actually determine the value for “a + b.” Once you know that you can divide both sides of the equation “3a + 3b = 234” by 3 and get a value for “a + b” then you do not need to actually make the calculation. Either the average will be less than 40 or it will not be, but in either case you will have a consistent answer.

Statement 2: This statement does not provide any fixed values for a or b and so it cannot be determined if the average of a + b will be less than 40. This statement is not sufficient.

The answer is A.
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Re: Is the average (arithmetic mean) of a and b less than 40? [#permalink]

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New post 21 Dec 2016, 16:46
Nice Question
Here is my solution to this one =>


\(Mean = \frac{Sum}{#}\)
Hence a+b/2<40
So a+b<80


We need to check if the sum of a and b is less than 80 or not

Statement 1-->
3a+3b=2*117
Hence a+b=2*39 => 78

Sufficient => YES

Statement 2-->
5a=b
1,5=> YES
10000,50000=> NO


Hence Not sufficient

Hence A

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Re: Is the average (arithmetic mean) of a and b less than 40? [#permalink]

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New post 06 Aug 2017, 13:06
i don't understand why ST 2 is insufficient. the way i see it:


(2) b=5a. --> \(\frac{6a}{2}\)<40 --> 6a <80 --> a~13. OK, plug in now: b=5(13); b=65.
- now, what is a+b? ~13 +65 = ~78. which is clearly under 80.

where am i going wrong here?

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Re: Is the average (arithmetic mean) of a and b less than 40?   [#permalink] 06 Aug 2017, 13:06
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Is the average (arithmetic mean) of a and b less than 40?

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