What is the addition rule of probability?
PICTURE THIS: HOW TO EXPLAIN IT
Simple meaning
For any two events, P(A or B) equals P(A) plus P(B) minus P(A and B) so the overlap is not counted twice.
WHY — Probability instead of guessing?
Why interviewers care about Probability:
who only read docs from people who shipped.
and tied to Data Science work.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1For any two events,
P(A or B) equals P(A) plus P(B) minus P(A and B) so the overlap is not counted twice.
- 2If A and B
cannot happen together, the intersection is zero and you simply add.
- 3This rule is the
basis for union metrics such as users who converted or churned.
- 4Give an example
One tiny concrete case you can say aloud.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
For any two events, P(A or B) equals P(A) plus P(B) minus P(A and B) so the overlap is not counted twice. If A and B cannot happen together, the intersection is zero and you simply add.