BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

During an experiment, some water was removed from each of

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Legendary Member
Posts: 2499
Joined: Sun Oct 29, 2017 2:04 pm
Followed by:6 members

During an experiment, some water was removed from each of

by swerve » Mon Dec 30, 2019 11:28 am
During an experiment, some water was removed from each of the 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 (arithmetic mean) volume of water in the tanks at the end of the experiment was 63 gallons.

The OA is A

Source: GMAT Prep
Top
Source: — Data Sufficiency |
Legendary Member
Posts: 2214
Joined: Fri Mar 02, 2018 2:22 pm
Followed by:5 members

by deloitte247 » Sun Jan 05, 2020 7:49 am
What was the standard deviation if water at the end of the experiment?
-There are 6 water tanks
-Standard deviation at the beginning of the experiment = 10 gallons
Statement 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.
If each term or element in a set is increased or decreased by the same percent or constant value, the standard deviation will increase or decrease by the same percent or constant value.
So, if 30% of water is removed from each tank, the standard deviation will decrease by 30%.
Therefore, the standard deviation at the end of the experiment = 10 - (30% of 10) = $$10-\left(\frac{30}{100}\cdot10\right)=10-3=7$$
Statement 1 is, therefore, SUFFICIENT.

Statement 2: The average (arithmetic mean) volume of water in the tanks at the end of the experiment was 63 gallons.
$$S\tan dard\ deviation=Summation\left(x_n-u\right)^2$$
This is how far the value of each element/tank is from the mean.
Since we do not know the exact volume of water in each tank, statement 2 is NOT SUFFICIENT.
Therefore, only statement 1 alone is SUFFICIENT, hence, the correct answer is option A.
Top
Post new topic Post Reply
• Page 1 of 1