math

A true-false test consists of 15 items.
(a) If Chris does not study at all and guesses each and every item in the test, describe the probability model for the number of correct guesses.
(b) What is the probability that Chris gets 80% or more for the test?

Not sure how to do a). Not sure if i did b) correct.



b) he must get 12 right or 13 right or 14 right or 15 right
= C(15,12)(1/2)^12 (1/2)^2 + C(15,13)(1/2)^13(1/2) + C(15,14) (1/2)^14+C(15,15)(1/2)^15
= 0.0426%

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asked by susan
  1. (a) it is a normal distribution (bell curve)n with the most likely score being half right (or wrong)

    you could plot the points using your binomial distribution from part (b)

    (b) the exponents in an individual term should sum to 15
    only your last term does that
    otherwise, looks okay

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    posted by Scott

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