water

[shibal]

Some water was removed from each of 6 tanks. If standard deviation of the volumes of water at the beginning was 10 gallons, what was the standard deviation of the volumes at the end?
a. For each tank, 30% of water at the beginning was removed
b. The average volume of water in the tanks at the end was 63 gallons

oa A

[ssmiles08]

1) standard deviation decreases by 30%. so sufficient.

2) Insufficient b/c we don't know how much water may be taken out of EACH tank, since the standard deviation is really based on difference b/w the mean and each point away from the mean.

(A)

[aj5105]

Check this link, Shibal.

https://www.beatthegmat.com/gmat-prep-qu ... 34898.html

[electrico]

1. Since, there is uniform change in the data, SD will not change.

So, A is sufficient.

2. It just give the avg volume.,..no info on the actual data/SD...

not enough..


So, Answer is A.

[wetandfire]

I am on the bandwagon that the SD will change.

If 1 tank is 10, and the other is 20 and the other is 30, there is our 10 SD. If we take 30% away from all 3 we will be left with
10 - 3 = 7, 20 - 6 = 14, and 30 - 9 = 21. Our standard deviation is now 7.