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