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What is the sum of the terms in a sequence of consecutive...

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by BTGmoderatorLU » Fri Nov 03, 2017 9:19 am
What is the sum of the terms in a sequence of consecutive multiples of 3?

(1) There is an odd number of terms in the sequence.

(2) The average of the sequence is zero.

The OA is B.

Please, can any expert explain this DS question? I need help to solve it. Thanks.
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Source: — Data Sufficiency |
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by DavidG@VeritasPrep » Fri Nov 03, 2017 9:57 am
LUANDATO wrote:What is the sum of the terms in a sequence of consecutive multiples of 3?

(1) There is an odd number of terms in the sequence.

(2) The average of the sequence is zero.

The OA is B.

Please, can any expert explain this DS question? I need help to solve it. Thanks.
Statement 1: Clearly not sufficient.

Case 1: {3, 6, 9} --> sum. = 18
Case 2: {3, 6, 9, 12, 15} --> sum = 45

Statement 2: We know that Sum = Average * Number Terms.
If the Average = 0, then we have Sum = 0 * Number Terms = 0. So the Sum must be 0. We have a unique value. Sufficient. The answer is B
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