30% of the volume of water that was in the tank at the beginning of the experime

[Take GMAT Team]

During an experiment, some water was removed from each of 6 water tanks. If the standard deviation of the volumes of water in the tanks at the beginning of the experiment was 10 gallons, what was the standard deviation of the volumes of water in the tanks at the end of the experiment?

1) For each tank, 30% of the volume of water that was in the tank at the beginning of the experiment was removed during the experiment.
2) The average (mean) volume of water in the tanks at the end of the experiment was 63 gallons.

Please provide details.

[720onGMAT]

1) is sufficient enough A is the answer

[chandu822]

SD is the measure of dispersion of the data.

1. 30 % of the original volumr is removed every time.

 If accurately 30% is removed every time there wont be any deviation at all from the mean.

NOT SUFFICIENT

2. Mean at the end of experiment is x

Again no data around mean is provided

NOT SUFFICIENT

Combinining all the info provided still doesnt give any data around mean.

Hence answer is E.

Am I in the right direction?

[rashiyadav24]

You are probably corect in your understanding but even that leaves the first option SUFFICIENT. Beacuse it tells us that no deviation from the mean has occured. The mean after the experiment would consequently be reduced by 30% and so would the volume in each tank keeping the SD same.

[Take GMAT Team]

Right answer.