Question

Three rats in a lab are injected a type of medicine. The independent probabilities for each rat exhibiting side effects are 0.5, 0.4 and 0.3 respectively.

Find the probability distribution formula for this problem with random variable X: the number of rats exhibiting side effects (out of 3)​

Answer 1

Explanation:

There are four possible values of X: 0 rats show side effects, 1 rat shows side effects, 2 rats show side effects, or all 3 rats show side effects.

Probability X = 0:

P = (1 − 0.5) (1 − 0.4) (1 − 0.3)

P = 0.21

Probability X = 1:

P = (0.5) (1 − 0.4) (1 − 0.3) + (1 − 0.5) (0.4) (1 − 0.3) + (1 − 0.5) (1 − 0.4) (0.3)

P = 0.44

Probability X = 2:

P = (0.5) (0.4) (1 − 0.3) + (0.5) (1 − 0.4) (0.3) + (1 − 0.5) (0.4) (0.3)

P = 0.29

Probability X = 3:

P = (0.5) (0.4) (0.3)

P = 0.06