紧急求助GMAT数学题

bosfashion

during an experiment, some water was removed from each of 6 water tanks. if the standard deviation of the volumes of the 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 ank, 30 percent of the volume of water that was in the tank at the beginning of experiment was removed   during experiment

(2)the average (arithmetic mean) volume of water in the tanks at the end of experiment was 63 gallons

A. 1 is sufficient alone and 2 is not sufficient alone

B. 2 is sufficient alone and 1 is not sufficient alone

C. Both together are sufficient, each alone is not sufficient

D. Both alone is sufficient

E. Not sufficient at all

梅飞色舞

答案A。