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What is the average of ten numbers?

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by swerve » Sat Nov 18, 2017 2:09 pm
What is the average of ten numbers?

1) Nine of the numbers sum to 45.
2) One of the numbers is 15.

The OA is E.

Please, can any expert explain this DS question for me? I have many difficulties to understand why that is the correct answer. Thanks.
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by Jay@ManhattanReview » Mon Dec 11, 2017 10:34 pm
swerve wrote:What is the average of ten numbers?

1) Nine of the numbers sum to 45.
2) One of the numbers is 15.

The OA is E.

Please, can any expert explain this DS question for me? I have many difficulties to understand why that is the correct answer. Thanks.
1) Nine of the numbers sum to 45.

We do not know the value of the tenth number. Insufficient.

2) One of the numbers is 15.

We do not know anything about the other nine numbers. Insufficient.

(1) and (2) together

If the tenth number = 15, then the average of the ten numbers = (45 + 15)/10 = 6; however, if 15 is one of the nine numebrs, we do not know the value of the tenth number. Insufficient.

The correct answer: E

Hope this helps!

-Jay
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