It is estimated that one fourth of the general population has blood type a+. a sample of nine people is selected at random. (round your answers to four decimal places.) (a) what is the probability that exactly five of them have blood type a+?

1/4 of the population is A+ 

if you wanted 5/9 to have that blood type you would need to make an equation using 1/4 and 5/9.

5/9 x 1/4  = 5/36 or 0.139 

You can verify because of all 9 had the A+ you can do the same equation but with 9/9 and 1/4

9/9 x 1/4 = 9/36 which is 0.25 or 1/4