This is my question for my homework: Of 30 patients in a waiting room, 50% have colds, 20% have the flu, and 10% have both.

This is my question for my homework:

Of 30 patients in a waiting room, 50% have colds, 20% have the flu, and 10% have both. What is the probability that a patient picked at random has a cold or the flu?

I know I am suppose to use P( A or B)= P(A)+ P(B) but I'm not sure how I am suppose to do that.