Homework Help: math

Posted by Katherine on Wednesday, April 21, 2010 at 4:50pm.

you take a three-question multiple-choice test.each question has four choices.you dont know any of the answers. what is the experimental probability that you will guess exactly two out of three correctly

please help me i am confused

math - Reiny, Wednesday, April 21, 2010 at 4:52pm
right = r
wrong = w

so you want
rrw
rwr
wrr
each of the above has a prob of 1/4 x 1/4 x 3/4 = 3/16

so the prob of getting 2 out of 3 correct is 3(3/16) = 9/16
correction - maths - Reiny, Wednesday, April 21, 2010 at 4:54pm
that should have said:

each of the above has a prob of 1/4 x 1/4 x 3/4 = 3/64

so the prob of getting 2 out of 3 correct is 3(3/64) = 9/64

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