THE NORMAL DISTRIBUTION Lesson 2
Starter: Find P (Z<1.63) To do this we begin with a sketch of the normal distribution. We then mark a line to represent Z=1.63 P(Z<1.63) is the area under the curve to the left of a. We now use the table to look up this probability P(Z<1.63) =
Remember this from last lesson! Note this result.. P(Z>a) = 1-P(Z<a)
And we found this really useful result P(Z<-a) = 1 - P(Z<a)
Objectives Finding the value of Z from a given probability.
Points to note P(Z<a) is greater than 0.5 a > 0 P(Z<a) is less than 0.5 a <0
Points to note P(Z>a) is less than 0.5 a > 0 P(Z>a) is greater than 0.5 a < 0
Ex 1 Find the value of a such that P(Z<a)=0.7852
Use the table P(Z<a) = a = 0.79 a
Ex 2 Find the value of a such that P(Z>a)=0.01 P(Z>a) = 0.01 P(Z<a) = Look up this result is in the main table. It’s not there! Instead look at the table of Percentage Points to see if p=0.01 is listed. P(Z>a) = 0.01 a = a
Ex 3 Find the value of a such that P(Z>a)= a a P(Z>a) = P(Z a) = = So from the main table a = 1.86
Ex 4 Find the value of a such that P(Z<a) = The table only lists values for z>0 so we need to reflect the problem in the vertical axis… P(Z<z) = 1 – = From the table z = 2.06 Therefore a = p= p= a z
Further Learning: Read through Example 2 on P180 Do Ex 9B on P181