1) P(A) = 50%
P(B) = 50%
P(A or B) = ____
P(A and B) = 0%
2) A and B are independent events.
P(A) = 0.35
P(B) = _____
P(A and B) = 0.2275
1) The equation for determining the either/or probability of overlapping events is: P(A or B) = P(A) + P(B) - P(A and B). As you can see, you must subtract out the probability of the overlapping event to get the right answer.
2) If the events are independent, the probability of both/all events occurring is determined by multiplying the probabilities of the individual events.