the proportion of citizens who wish bush was still president

the proportion of citizens who wish bush was still president is .9. what is the probability that there will be 85 or more Bush wishers in a class of 100?

Solution

Mean ( np ) =90
Standard Deviation ( npq )= 100*0.9*0.1 = 3
Normal Distribution = Z= X- u / sd                   
P(X < 85) = (85-90)/3
= -5/3= -1.6667
= P ( Z <-1.6667) From Standard Normal Table
= 0.0478                  
P(X > = 85) = (1 - P(X < 85)
= 1 - 0.0478 = 0.9522