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# During an experiment, some water was removed from each of 6

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Manager
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During an experiment, some water was removed from each of 6 [#permalink]

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19 Mar 2006, 15:18
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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 the water in the tanks at the end of the experiment?

(1) For each tank, 30 percent of the volume of watwer that was in the tank at the beginning of the experiment was removed during the experiment.

(2) The average (arithemtic mean) volume of water in the tanks at the end of the experiment was 63 gallons.
Manager
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19 Mar 2006, 15:40
OA is A.

Can you guys explain?
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19 Mar 2006, 15:43
kook44 wrote:
OA is A. Can you guys explain?

if you add (or take out) same % amount of the water from each of the tanks, the SD remains the same because the deviation from the mean remains the same.
19 Mar 2006, 15:43
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