SAT Math Question : Probability (basic)

 

The SAT math section includes simple questions involving probability, which refers to the statistical chances of an event occurring (or not occurring). By definition, probability ranges from  to  (Probability is never negative, and it’s never greater than ). An event with a probability of  is impossible, and an event with a probability of  is certain. You can express probability either as either a fraction or a percent. Here is the basic formula:

 

To calculate the probability of an event NOT occurring, just subtract the probability of the event occurring from . Referring to the preceding example, the probability of NOT selecting a face card would be 

 

An SAT probability problem might involve the probability of two independent events both occurring. Two events are “independent” if neither event affects the probability that the other will occur. Here are two general situations:

  • The random selection of one object from each of two groups (for example, the outcome of throwing a pair of dice)
  • The random selection of one object from a group, then replacing it and selecting again (as in a “second round” or “another turn” of a game)

To determine the probability of two independent events both occurring, multiply individual probabilities.

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