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New member
Jan 31, 2011
Total Cholesterol in children aged 10 to 15 years of age is assumed t follow a normal distribution with a mean of 191 and a standard deviation of 22.4.
a) what proportion of children 10 to 15 years of age have total cholesterol between 180-190?
b) what proportion of children 10 to 15 years of age would be classified as hyperlipidemic (assume that hyperlipidemia is defined as a total cholesterol level over 200)?
c) what is the 90th percentile of total cholesterol?

Ok, so that is the question.

I understand that there are 6 study persons..10,11,12,13,14,& 15 year old's. I plugged in the mean given and the standard deviation that was given...what I don't understand is how do I get the other information...I got the cholesterol information from the first question but am not sure if it correct. If anybody is able to help me with this problem I would greatly appreciate it. I took this class as a filler, it isn't need for my master's degree but I am not able to drop it at this time.

x Cholesterol Mean standard deviation probability
10 180 191 22.4 11
11 185 191 22.4 6
12 190 191 22.4 1
13 195 191 22.4 -4
14 200 191 22.4 -9
15 200+ 191 22.4 not sure what this number would be or if the other numbers are correct.


Staff member
Apr 12, 2005
b) looks like it might be the easiest.

Calculate the z-score

(200-191)/22.4 = 9/22.4 = 0.402

A VERY ROUGH empirical rule might suggest that we should be somewhere in the neighborhood of 0.50 - 0.4*0.34 = 0.50 - 0.14 = 0.36

A closer look at a table or calculator (using total values of the cummulative density function) provides 1.00 - 0.66 = 0.34

The emperical rule wasn't too far off.

Part a) is very similar. It's just in 2 pieces. Let's see what you get. Part c) is backwards, but is the same principle.