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Calculating from Standard Deviation and Mean

7K views 3 replies 4 participants last post by  whocares13 
#1 ·
A study of 400 patients hospitalized with diabetes mellitus related complications shows that the serum cholesterol level is a normally distributed variable with a mean value of 220mg/dl and standard deviation of 10 mg/dl. Based on study result, how many patients do you expect to have serum cholesterol level > or equal to 240mg/dl in this study??

a) 2
b) 10
c) 20
d) 64
e) 120

Please reply with explanation
 
#4 · (Edited)
Ans is b) 10

Explanation: Mean is 220, so you keep the center value 220. SD is 10, so >or=240 will lie above 2 SD.

As you know -1 to +1 = 68, and -2 to +2 = 95 and -3 to +3 = 99.7 per Gaussian Distribution. And as a whole will be100% ofcourse.

So calculation --> 50%(Half of 100%) - 34(half of 68) - 13.5(half of 27) =2.5%

This means 2.5% of people have BS >or= 240.

We have total pt = 400. SO, no. of pt having BS >or= 240 === 2.5% of 400. i.e. 10

Hope I was clear. :)
 
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