SAT Math: Conditional Probability (Given Information)
30+ practice questions in Praczo
The concept, explained
- 1
Conditional probability asks for the probability of A given that B has already happened or is known to be true. P(A | B).
- 2
The key is restricting the denominator. You are no longer looking at the whole total, but ONLY the total for group B.
- 3
Often tested using a two-way frequency table. Find the row or column of the "given" condition, then find the specific target within that subset.
- 4
Wording indicators: "If a person is chosen...", "Given that...", "Of the participants who...".
- 5
Do not use the grand total in the denominator if there is a condition.
- ✗ Using the grand total as the denominator instead of the row or column total specified by the condition.
- ✗ Confusing P(A given B) with P(B given A) resulting in swapping the numerator/denominator logic.
SAT-style practice
A table shows 50 students. 20 are juniors and 30 are seniors. 12 juniors take calculus and 15 seniors take calculus. If a student who takes calculus is randomly selected, what is the probability they are a junior?
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