Find the probability that the student gets exactly 15 correct answers.

Mathematics
Tutor: None Selected Time limit: 1 Day

A student answers all 48 questions on a multiple choice test by guessing. Each question has four possible answers, only one of which is correct. Find the probability that the student gets exactly 15 correct answers. Use the normal distribution to approximate the binomial distribution. 

May 1st, 2015

 Find the probability of giving 5 correct answers.
P(x=5) = (1/4)^5 = 0.000976...
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B. Find the probability of giving 5 incorrect answers.
P(x=0) = (3/4)^5 = 0.237...


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C. Find the probability of giving at least 1 correct answer. 
P(x>=1)= 1 - P(x=0)
= 1 - 0.237...
= 0.76269....
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D. Find the probability of giving exactly 1 correct answer.
P(x=1) = 5C1(1/4)(3/4)^4 = 5*(1/4)(0.3164...) = 0.39550....
1/5=0.39550
15/48=?
=0.6180

May 1st, 2015

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