probabilities

A multiple choice test has 16 questions. Each question has 4 possible answers with
only one is correct. Assume that all questions are answered and the probability to
answer any question correctly is 0.25. Let X be the number of questions answered
correctly among 16.
1. What model would you propose for X ? Compute E(X) and V (X).
2. What is the probability that at least 4 questions are answered correctly in the
test ?
3. What is the probability that 7, 8, 9, or 10 questions are answered correctly ?

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  1. Sarah got 80% on her math quiz. If she answered 12 questions correctly, how many question were on the test?

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  2. Fhshnanxnsan

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