The fourth grade at school X is made up of 300 students who have a total weight of 21,600 pounds. If the weight of these fourth graders has a normal distribution and the standard deviation equals 12 pounds, approximately how many of these fourth graders weigh more than 84 pounds?
1. 12
2. 16
3. 36
4. 48
5. 60
Standard Deviation
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- Brent@GMATPrepNow
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This question is out of scope; normal distributions are not tested on the GMAT.
Cheers,
Brent
Cheers,
Brent
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Students 300
Weight 21600
Mean = 72
First SD = 72+12 = 84
The percentage corresponding to 84+ --> 13.5 + 2.5 approx = 16%
So, 16% of 300 = 48
Answer [spoiler]{D}[/spoiler]
Weight 21600
Mean = 72
First SD = 72+12 = 84
The percentage corresponding to 84+ --> 13.5 + 2.5 approx = 16%
So, 16% of 300 = 48
Answer [spoiler]{D}[/spoiler]
R A H U L
- theCodeToGMAT
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I will draw to explain..ani781 wrote:RAHUL, how did you arrive at the 16 ? Can you pls clarify.
![Image](https://s8.postimg.cc/fron9ds4x/solution.jpg)
The percentageS marked in this diagram are FIXED.
S.D. is basically a deviation from MEAN.. and FIRST, SECOND & THIRD Deviation tells the distribution of people at each SD Interval.
For example: First SD from MEAN = 34%(Scores above Mean) + 34%(Scores below Mean)
Now, the questions asks us to find students above 84(that means right side of the graph).. we know SD = 12.. we found mean as 72
First SD = 72 + 12 = 84
All the students after First S.D. will have weight above 84...
So, (50 - 34 ) = 16%
Is it fine now?
R A H U L