posted by peter .
A jar contains 2 red balls, 2 blue balls, 2 green balls and 1 orange ball. Balls are randomly selected, without replacement, until 2 of the same colour are obtained. Calculate the probability that more than 3 balls must be selected.
"More than 3 balls" = either 4 or 5 balls.
If the events are independent, the probability of both/all events occurring is determined by multiplying the probabilities of the individual events.
Either-or probabilities are found by adding the individual probabilities.