-
teejaycrown
- Senior | Next Rank: 100 Posts
- Posts: 30
- Joined: Sun Oct 14, 2012 1:34 pm
- Followed by:1 members
Typically, the GMAT uses the term "units of standard deviation"teejaycrown wrote:For a certain examination, a score of 58 was 2 standard deviation below the mean, and a score of 98 was 3 standard deviation above the mean. What was the mean score for the examination
74, 76, 78, 80, 82.
So, if the SD is 4, then 1 unit of SD = 4
Similarly, 2 units of SD = 8
And 1.5 units of SD = 6
If the mean is 10 and the SD is 4, then we say that 18 is 2 units of SD above the mean since 10 + 2(4) = 18
Similarly, we say that 6 is 1 unit of SD below the mean since 10 - 4 = 4
For your question, we can let M=mean and let D=the standard deviation
So, 58 is 2 standard deviations below the mean translates into M - 2D = 58
and 98 is 3 standard deviations above the mean translates into M + 3D = 98
When we solve this system of equations, we get M=74 and D=8
So the answer is A
Cheers,
Brent
