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

Redeem

Standard Deviation

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Newbie | Next Rank: 10 Posts
Posts: 2
Joined: Tue Oct 07, 2008 10:46 am
Location: Halifax

Standard Deviation

by dham1234 » Mon Oct 20, 2008 4:27 pm
This is a question I am having trouble with:
If 58 is 2 standard deviations below the mean and 98 is 3 standard deviations above the mean then what is the mean?
Please help.
thanks.
Top
Source: — Problem Solving |
Master | Next Rank: 500 Posts
Posts: 105
Joined: Tue Jul 15, 2008 7:03 pm
Thanked: 5 times

by pre-gmat » Mon Oct 20, 2008 6:04 pm
58=Mean - 2SD
98= mean +3SD

from the 2 equations you get:

174=3 mean - 6SD
196= 2Mean + 6SD

Adding the equations:

370= 5 Mean
Mean = 74
Top
GMAT Instructor
Posts: 1223
Joined: Thu May 01, 2008 3:29 pm
Location: Los Angeles, CA
Thanked: 185 times
Followed by:15 members

by VP_Jim » Mon Oct 20, 2008 9:28 pm
Here's another way:

We know that there are 5 standard deviations between 58 and 98, a difference of 40. Therefore, one standard deviation is 40/5 = 8.

Now we can just add:

58 is two standard deviations below, so 58+8+8 = 74.

Or:

98 is three standard deviations above the mean, so 98-8-8-8 = 74.

Hope this helps!
Jim S. | GMAT Instructor | Veritas Prep
Top
Post new topic Post Reply
• Page 1 of 1