No formula is associated with this answer.
Work Step by Step
To start this problem, a probability tree should be drawn. The probability tree is attached below. a.) The first way to test positive for pregnancy is to be pregnant and the probability is (0.1)(0.98) = 0.098. The second way is to not be pregnant and test positive and the probability is (0.9)(0.01) = 0.009. This means that testing positive is 0.098 + 0.009 = 0.107 b.) P(test positive) = (0.05)(0.98) + (0.95)(0.01) = 0.49 + 0.095 = 0.0585