Novice90 wrote:

quantumliner wrote:

Statement 1: Decreasing the number in a set by a constant, does not change the Standard Deviation of the set of numbers.

In this case since the amount of water decreased in each tank is a constant value. The standard deviation does not change. So we know that Standard Deviation was same at the end of the year.

Statement 1 is sufficient.

Statement 2: In this case the amount decreased is 20% of each tank, which is a variable amount for each tank (depending on the water in each tank. Now if each tank had the same quantity of water, then decrease would be constant and the Standard Deviation would remain the same. But the tanks may also have different quantities of water, resulting in a different Standard Deviation at the end of the year. Since we do not have that information about the quantity of water in each tank, This Statement is not sufficient.

Answer is A

Wouldn't Statement 2 also be sufficient to answer the question.

Given that all volumes are reduced by the same percentage amount, the SD would also reduce by a particular amount and would never be the same as the starting standard deviation

Hey

If the old SD was 0, then new SD will also be 0 even if the it is reduced by 20%

But if old SD was x, then new SD will also change to 0.80*x

So Statement 2 is insufficient

Hope this clears your doubt

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