Question

Nathan had an infection, and his doctor wanted him to take penicillin. Because Nathan's father and paternal grandfather were allergic to penicillin, Nathan has a 75% chance of having the same allergy. The doctor performed a skin test to see whether Nathan would react to it. The test is 98% accurate. If the test predicts that Nathan is not allergic to penicillin, what is the probability after the test that Nathan is not allergic to the drug?
A) 0.1135

B) 0.2450

C) 0.9423

D) 0.9932​

Answer 1

Nathan has a 25% chance of NOT being allergic to the drug. And then that 25% is 98% accurate so:

25% x 98%

0.25 x 0.95 (changed to decimals)

= B) 0.2450