CSCA Exam › Mathematics › Probability and statistics Reviewed CSCA Mathematics question · Easy A bag contains 4 red marbles, 3 blue marbles, and 5 green marbles. If one marble is drawn at random, what is the probability that it is not blue? 3/12 9/12 5/12 4/12 Show the answer and explanation Correct answer B. 9/12
Principle or equation Probability of an event = number of favorable outcomes / total number of outcomes. The complement rule: P(not blue) = 1 - P(blue).
Why this answer is correct Total marbles = 4 + 3 + 5 = 12. Blue marbles = 3, so P(blue) = 3/12 = 1/4. Therefore P(not blue) = 1 - 1/4 = 3/4 = 9/12.
Example If a bag has 2 red and 2 blue marbles, P(not blue) = 1 - 2/4 = 1/2.
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