For Exercises 4.14 and 4.15, see pages 180–181; for 4.16 to 4.20, see pages 183–184; for 4.21 to 4.23, see pages 185–186; for 4.24, see page 187; for 4.25 and 4.26, see page 189; and for 4.27 to 4.29, see page 190.

Question 4.20

4.20 Grading Canadian health care.

Annually, the Canadian Medical Association uses the marketing research firm Ipsos Canada to measure public opinion with respect to the Canadian health care system. Between July 17 and July 26 of 2013, Ipsos Canada interviewed a random sample of 1000 adults.3 The people in the sample were asked to grade the overall quality of health care services as an A, B, C, or F, where an A is the highest grade and an F is a failing grade. Here are the results:

Outcome Probability
A 0.30
B 0.45
C ?
F 0.06

These proportions are probabilities for choosing an adult at random and asking the person's opinion on the Canadian health care system.

  1. What is the probability that a person chosen at random gives a grade of C? Why?
  2. If a “positive” grade is defined as A or B, what is the probability of a positive grade?