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If a is a positive number less than 10, is c greater than the average

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If a is a positive number less than 10, is c greater than the average  [#permalink]

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New post 09 Jan 2018, 23:39
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A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

53% (02:11) correct 47% (01:15) wrong based on 30 sessions

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Re: If a is a positive number less than 10, is c greater than the average  [#permalink]

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New post 10 Jan 2018, 00:33
Bunuel wrote:
If a is a positive number less than 10, is c greater than the average (arithmetic mean) of a and 10?

(1) c = 4a
(2) c is less than 10.


Average of a & 10 = (a+10)/2. It will lie exactly in the middle of a & 10, on the number line. We have to answer whether c > (a+10)/2 or not.

(1) c = 4a. So we need to know whether 4a > (a+10)/2 Or 8a > a+10 Or Is a > 10/7. But since we dont know whether a > 10/7, so we cant say whether c is greater than average of a & 10. Insufficient.

(2) c < 10. This will tell us nothing about the required question. Insufficient.

Combining the statements, c = 4a and c < 10. If a=1, then c=4, average of a & 10 = 5.5. Here c is lesser than the average of a&10.
But if a=2, c=8, average of a & 10 = 6. Here c is greater than the average of a&10. So Insufficient.

Hence E answer
Re: If a is a positive number less than 10, is c greater than the average &nbs [#permalink] 10 Jan 2018, 00:33
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