In a 200 m swimming race between 8 boys, the probability of Omar winning the race if he is in one of the two outside lanes is 1/4. If he is in any of the other lanes, the probability of Omar winning is 1/3.
If the lanes are drawn at random, what is the overall probability of Omar winning the race?
Consider that there are 2/8 probability of getting an outside lane. To get the probability that both (all) events would happen, you need to multiply the probabilities of the individual events (2/8*1/4).
Do the same for the 6 inside lanes.
However, he can be placed in either the inside or outside lanes. In the case of "either-or" probabilities, you add the probabilities of the individual events.
I hope this helps. Thanks for asking.