

Practice Problem:
Probability and Normal Distribution
 Problem
 For the normal distribution N(50,20)  that is
that has a mean of 50 and a standard deviation of
20  find X such that 71.57% of the area under the
curve is to the left of X.
 Answer
 The ZScore is .57 because it has .7157 of the
area to the left of it.
This means that X is .57 population standard
deviation units above the population mean.
 Therefore:
X = PopMean + .57 PopStDv
X = 50 + .57*20
X = 50 + 11.4
X = 61.4
