statistics and probability

It is known that an exam scores of students in STAT 2507 follow a normal distribution with a mean
of 70% and a standard deviation of 9%.
(A) If a student must obtain a mark of 50% to pass the exam, what proportion of students fail the exam?
(B) What is the probability that a randomly selected student will score between 65% and 85%?
(C) What is the minimum score required for a student to be in the top 10 percent of the class?
(D) What is the probability that a student will get exactly 70%?

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  1. Familiarize yourself with a normal distribution table or online calculator, such as the one at
    http://stattrek.com/Tables/Normal.aspx

    (A) 1.3%
    (B) Subtract P(x<65) from P(x<85)
    (C) Find the value of X for which P(x<X) = 0.90 I get 81.5%
    (D) Take the difference between getting a score of 70.5% and 69.5%

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