Last Updated on May 11, 2023
GMAT OFFICIAL GUIDE PS
Solution:
We are given that the probability that event M will not occur is 0.8 and the probability that event R will not occur is 0.6, and that events M and R cannot both occur.
We need to determine the probability that either event M or event R will occur.
The probability that event M will occur is 1 – 0.8 = 0.2 = 1/5
The probability that event R will occur is 1 – 0.6 = 0.4 = 2/5
Recall that the formula for the probability of event A or event B occurring is P(A or B) = P(A) + P(B) – P(A and B); therefore:
P(M or R) = P(M) + P(R) – P(M and R).
Since we are told that events M and R cannot both occur, that means P(M and R) = 0 and thus the probability that either event M or event R will occur is:
P(M or R) = 1/5 + 2/5 – 0 = 3/5.
Answer: C
