in a multiple choice exam with three possible answers for each of the five questions.

Question

in a multiple choice exam with three possible answers for each of the five questions.

 

a) what is the probablity that a student would get four or more correct answer just by quessing.

 

b) A student can improve his changes to find the right answer to each question by studying. For example if a student finds the time to study for her exam, she can give the right answer to each question with probability 2/3. Otherwise, she has to guess the answer with guessing. If the probability that  girl finds the time to study for the exam is 3/5. What is the probability that she will get four or more correct answer? and

 

in part b) what are the expected number of questions that she will answer correctly?

Answer 1

a)  (₅C₄)(1/3)⁴(2/3)¹ + (₅C₅)(1/3)⁵(2/3)⁰ 

 

       (5)(1/81)(2/3) + (1)(1/243)(1)

 

            10/243  +  1/243 = 11/243 ≈ 0.0453

 

 

 

Unfortunately, I am out of time till this afternoon - I'll try to get back to this later today.