Statistics Question: Cholesterol levels are normally distributed with a mean of 170 and a SD of 30.

Question

Find the probability a randomly selected individual has a cholesterol level greater than 225. 

 

The answer is = 0.0336 But i am not sure how to find this answer. 

Answer 1

The answer you cited is correct. I used the command normalcdf(225,10⁹,170,30) on a TI-83 DISTRibutions menu.

 

The 4 parameters of this command are a,b,μ,σ respectively.

 

If you're using a Standard Normal Distribution, you simply look for the area under the curve corresponding to Z₂₂₅ and beyond; this z-score is 1.83333.

 

Z₂₂₅ = (225 - 170) /30 using formula (X - μ) / σ.