A survey among freshmen at a certain university revealed that the number of hour

Question

A survey among freshmen at a certain university revealed that the number of hours spent studying the week before final exams was normally distributed with mean 25 and standard deviation 7. What is the probability that a randomly selected student spent between 35 and 40 hours studying? Write only a number as your answer. Round to 4 decimal places (for example 0.0048). Do not write as a percentage. Your Answer: The lifetime of a certain type of automobile tire (in thousands of miles) is normally distributed with mean 35 and standard deviation 5. Find the percentile corresponding to p = 59 % of the tire lifetimes. Write only a number as your answer. Round to two decimal places (for example: 0.81). Your Answer:

Explanation / Answer

mean =25 sd=7

find P(35<x<40)?

z score =mu-mean/sd

P(35<x<40) =P(35-25/7< z<40-25/7)

                   =p(10/7<z<15/7)

                  =P(z<15/7)-P(z<10/7)

          = p(z<2.142857143)-P(Z<1.428571429)    (see standard normal table)

                 =0.983938-0.923436

                  =0.0605

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