Combining probabilities

In the section entitled Qubits don’t plan ahead, we use rules of probability to form conclusions about entangled qubits. If you’re not familiar with these rules, this section is for you.

An outcome is one possible result from a randomly-conducted experiment. For example, you shuffle a standard, 52-card deck of playing cards. Then, you close your eyes and select one of the cards. One outcome of this experiment is that you pick the nine of hearts. Another outcome is that you pick the queen of spades. All in all, this experiment has 52 outcomes.

An event is a set of outcomes in a randomly conducted experiment. Again, pick one card from a shuffled, 52-card deck. Picking a red card is an example of an event because picking a red card means picking a card from the set of all hearts and diamonds. Picking a face card (jack, queen, or king) is another event. Picking an even-numbered card is an event. Picking either a 2 of clubs, a 10 of diamonds,...