ACT · Pre-Algebra · Elementary probability
Question act-q-00277
Medium Multiple choice Calculator OK
The question
A bag contains 3 red marbles and 6 blue marbles. If one marble is drawn at random, what is the probability that it is red?
- 6/9
- 3/6
- 3/9
- 6/3
Show answer & worked solution
Answer: 3/9
Worked solution. Probability = favorable outcomes / total outcomes = 3 / 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 a moderate position in the section — solidly within the range that separates a 600-band student from a 700-band student. Treat any miss in this subtopic as a signal to drill the subtopic page before you do another full practice test.