The high temperature in Chicago for the month of August is n

The high temperature in Chicago for the month of August is normally distributed with a
mean of 80 degrees and a standard deviation of 8 degrees.
a. Determine the percentage of days in August with a high temperature above 90
degrees
b. Determine the percentage of days in August with a high temperature below 60
degrees

Solution

Normal Distribution
Mean ( u ) =80
Standard Deviation ( sd )=8
Normal Distribution = Z= X- u / sd ~ N(0,1)                  
a)              
P(X > 90) = (90-80)/8
= 10/8 = 1.25
= P ( Z >1.25) From Standard Normal Table
= 0.1056                  
b)
P(X < 60) = (60-80)/8
= -20/8= -2.5
= P ( Z <-2.5) From Standard Normal Table
= 0.0062