CCSS.Math.Content.HSS-CP.B.7
The standard
Apply the Addition Rule, P(A or B) = P(A) + P(B) - P(A and B), and interpret the answer in terms of the model.
Common Core State Standards for Mathematics
What this standard means
Students need to find the chance that event A happens, event B happens, or both happen. They must add the two separate probabilities and subtract the overlap so it is not counted twice. They should use two-way tables, Venn diagrams, and short probability statements.
Mastery looks like spotting the word “or” as inclusive, unless the problem says otherwise. Students can explain the answer in context, not just give a decimal. Common trouble spots are double-counting the overlap, mixing up “and” with “or,” and forgetting to describe what the final probability means.
Ways to teach it
- Hands-on activity: Give pairs colored counters in overlapping hula hoops and have them count A, B, both, and A or B.
- Writing prompt: Explain why adding P(A) and P(B) can be too large when the events overlap.
- Quick assessment: Show a two-way table of 40 students and ask for P(sports or music), with one sentence of interpretation.
- Real-world connection: Use school survey data on students who have a job, play a sport, or both, then find the probability of job or sport.
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Related standards
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Find the conditional probability of A given B as the fraction of B's outcomes that also belong to A, and interpret the answer in terms of the model.
- CCSS.Math.Content.HSS-CP.B.8
(+) Apply the general Multiplication Rule in a uniform probability model, P(A and B) = P(A)P(B|A) = P(B)P(A|B), and interpret the answer in terms of the model.
- CCSS.Math.Content.HSS-CP.A.2
Understand that two events A and B are independent if the probability of A and B occurring together is the product of their probabilities, and use this characte...