Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 27 Jun 2016, 16:10

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

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

Author Message
Intern
Joined: 09 Dec 2006
Posts: 8
Followers: 0

Kudos [?]: 1 [0], given: 0

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

### Show Tags

17 Jan 2007, 09:22
00:00

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 1 sessions

### HideShow timer Statistics

This topic is locked. If you want to discuss this question please re-post it in the respective forum.

During an experiment, some water was removed from each of 6 water tanks. If the standards 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 percent of the volume of water that was in the tank at the beginning of the experiment was removed during the experiment
(2)The average (arithmetic mean) volume of water in the tanks at the end of the experiement was 63 gallons
Director
Joined: 17 Jul 2006
Posts: 714
Followers: 1

Kudos [?]: 11 [0], given: 0

### Show Tags

17 Jan 2007, 11:16

SD still same after removing 30 percent from each tank
Intern
Joined: 22 Sep 2006
Posts: 37
Followers: 0

Kudos [?]: 1 [0], given: 0

### Show Tags

17 Jan 2007, 11:30

St_Dev = SQRT[ ((a1- Avg)^2 + (a2 â€“ Avg)^2 + â€¦) / n]
Avg = (a1 + a2 + â€¦) / n

From A we can calculate the new average and st. deviation:
Avg_new = (0.7*a1 + 0.7*a2 + â€¦) / n = 0.7 * Avg

St_dev_new = SQRT[ ((0.7*a1 â€“ 0.7*Avg)^2 + â€¦) / n)]
= 0.7 * SQRT[ ((a1- Avg)^2 + (a2 â€“ Avg)^2 + â€¦) / n]
= 0.7 * St_dev

B is not sufficient
Display posts from previous: Sort by