ACT · Pre-Algebra · Elementary probability
Question act-q-00272
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The question
A bag contains 4 red marbles and 5 blue marbles. If one marble is drawn at random, what is the probability that it is red?
- 5/9
- 4/9
- 4/5
- 5/4
Show answer & worked solution
Answer: 4/9
Worked solution. Probability = favorable outcomes / total outcomes = 4 / 9.
Why each wrong choice is wrong. Common distractors compute the probability of the other color, or use the wrong color count in the numerator or denominator.
Test-day tactic. Probability is favorable over total. Total includes everything in the sample space, not just the unfavorable outcomes.
About this question type
Items ask for the probability of a single event, of compound independent events, or for "at least one" using the complement rule.
You will see a question shaped like this one on roughly every other official ACT form, typically at the back end of the section, where the score gradient is steepest. Treat any miss in this subtopic as a signal to drill the subtopic page before you do another full practice test.