In a group of 20 patients at a medical centre, 5 suffered from migraines. Two patients from the group of 20 were picked at random for a survey on the use of painkillers. What is the probability that both of the patients picked suffered from migraines?

Answer:

8) A

Out of 20 patients, 5 have migraine.
Probability of the first patient having migraine = ⁵⁄₂₀ = ¼

Since 1 patient with migraine is already picked, number of patients left with migraine = 5 – 1 = 4
Total number of patient remaining = 20 – 1 = 19
Probability of the second patient having migraine = ⁴⁄₁₉

Proabbaiilty of both patientes having migraine = ⁴⁄₁₉  x  ¼  =   ⁴⁄₇₆ = ¹⁄₁₉