Question

A dentist polls his patients and finds that 83 percent brush their teeth at least twice a day, 47 percent floss daily, and 19 percent brush at least twice a day and floss daily. What is the probability that a patient flosses daily, given that he or she brushes at least twice a day? Round to the nearest percent.

16%
23%
40%
57%

Answer 1

We want P(floss daily | brush ≥2/day) = P(both) / P(brush ≥2/day) = 0.19 / 0.83 ≈ 0.2289 ≈ 23%.

Answer: 23%