For equally likely outcomes, probability is favorable outcomes divided by all possible outcomes. In a conditional question, the condition determines the denominator.
Key Rules
Count the total outcomes in the relevant group.
Count the outcomes satisfying the requested event.
Use 1 minus the probability of an event to find its complement.
Common Mistakes to Avoid
Keeping the full population as the denominator after a condition restricts the group.
Confusing the chance of either of two events with the chance of both.
SAT Strategy Tips
→Read whether the question says “and,” “or,” or “given.”
→A probability must be between 0 and 1.
Example Question
A bag contains 5 red, 3 blue and 2 green beads. One bead is selected at random. What is the probability that it is not blue?
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