Your question is Probability Proof for Test Scenario. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Prove the probability of a test scenario.
Show the probability calculation clearly, state any assumptions, and explain the result in a way that can be checked step by step. If you use a test, specify the null and alternative hypotheses and the decision rule.