Question

The medical records for a class of 28 children show whether they had previously had
measles or mumps. The records show 22 have had measles, 13 have had measles and
mumps, and 27 have had measles or mumps. If one child from the class is selected at
random, determine the probability that he or she has had:
part a: measles part b: mumps but not measles part c: neither mumps nor measles.

Answer 1

Can help with a and c
a. 22/28 of class had measles, so this is probability 78.6%
c. 1/28 had neither so this is probability 1/28 = 3.6%

b. having mumps but not measles? 27 had mumps or measles, 22 had measles, leaving 5 who had mumps only? 5/28 = 17.9%.

Adds up to 28/28, so perhaps this is right.