Question

Which formula would you use to find out the probability of a doctor's patients being pregnant or not?

Answer 1

Answer: Complement Rule which is given by P(A) + P(A′) = 1

Explanation: According to the Complement Rule of probability the sum of probability of an event occuring and its complement is equal to 1. It is given by :

P(A) + P(A′) = 1

In the given question, the two events are mutually exclusive events (cannot occur simultaneously) so the complement rule holds true. An easy way to find out if the probability follows a complement rule is - the word 'NOT' is used (basically a negation to the prior statement).

So the doctor's patients can be pregnant or not -----> these are Mutually Exclusive events (as she cannot be pregnant and not pregnant at the same time) and the word 'Not'(negation) is used as well as 'OR' has been used ,so the sum of the probability of the 2 events is equal to 1, hence it follows the Complement Rule of Probability.