SAT Probability Questions
Chance read off a two-way table. Conditional probability restricts you to one row or column before you divide.
In short
- Probability is part of Problem-Solving and Data Analysis, about 15% of the scored Math questions: 5 to 7 on every test.
- Math questions from all four areas are mixed in each module and arranged from easiest to hardest.
- Part over whole is the trap Rivie's practice tests set most often in Probability questions.
Common traps
Most common first, from Rivie's ten practice tests.
Part over whole
Probability or proportion: the wrong choice uses part / part (e.g. boys / girls) instead of part / whole (boys / total).
The usual mistake: You read 'probability of selecting X' and divide by the wrong group, usually whichever group was named most recently in the prompt.
Conditional vs. marginal
P(A) is the marginal probability of A across the whole sample. P(A | B) is the conditional: A among the subset where B is true. The denominator is what changes.
The usual mistake: You divide by the total when the question filters to a subgroup. 'Of the people who voted, what fraction were under 30?' divides by voters, not by everyone.
Try a question
From Rivie's practice tests. Pick an answer to see why it is right or wrong.
A fair six-sided die is rolled once. What is the probability that the number rolled is greater than 4?
Video lessons
Free on YouTube, picked for this topic.