SOLUTION: a mathematics professor gives an "extra-credit" (bonus marks) problem on a test. if it is done correctly, 15 points are added to the test score, and if it is done partially correct

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Question 1160868: a mathematics professor gives an "extra-credit" (bonus marks) problem on a test. if it is done correctly, 15 points are added to the test score, and if it is done partially correctly, 5 points are added; otherwise 5 points are subtracted. suppose a student's probability of getting the problem completely right is 1/4, and only partially correct is 1/2. find the student's mathematical expectation E (expected value) for extra credit.
Answer by ikleyn(52776) About Me  (Show Source):
You can put this solution on YOUR website!
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    E = %281%2F4%29%2A15 + %281%2F2%29%2A5 - %281%2F4%29%2A5 = %2815+%2B+10+-+5%29%2F4 = 20%2F4 = 5 bonus marks.    ANSWER

Solved.