Math probability

Question

In a class of 28 students, 19 have a cat and 6 have a dog. There are 5 students who do not have a cat or a dog. What is the probability that a student who has a cat also has a dog?

Answer 1

19 students have cats, 6 students have dogs, 5 students have neither. Add that up you get 30. Therefore 2 students have both cats and dogs. The probability that a student has a cat and a dog is thus 2/28 = 1/14.