probability in biostatistics

Question

Drug A has probability of 0.67 of curing COVID-19 whenever it is administered. If drug A is administered 4 times, find the probability that drug A will cure COVID-19 when administered;

a) Exactly 2 times

b) At least 1 times

c) More than half of the times

Answer 1

p(0) = 0.33^4

p(1) = 4 x 0.67 x 0.33^3

p(2) = 4 C 2 x 0.67^2 x 0.33 ^ 2 = 6 x 0.67^2 x 0.33^2

p(3) = 4 x 0.67^3 x 0.44

p(4) = 0.67^4

a) p(2)

b) 1 - p(0)

c) p(3) + p(4)