Z Score and Probability

Question 1

In a class where the exam averages are normally distributed, the mean score is 75 and the standard deviation is 10. If you want to find out the probability that a randomly picked student has scored 85 or above, what is the z value that you should look up on the normal distribution table?

Question 2 According to a report by Scarborough Research, the average monthly household cellular phone bill is $73. Suppose local monthly household cell phone bills are normally distributed with a standard deviation of $11. a. What is the probability that a randomly selected monthly cell phone bill is less than $95? b. What is the probability that a randomly selected monthly cell phone bill is between $62 and $84?

Question 3 A Travel Weekly International Air Transport Association survey asked business travelers about the purpose for their most recent business trip. Nineteen percent responded that it was for an internal company visit. Suppose 950 business travelers are randomly selected. a. What is the probability that more than 20% of the business travelers say that the reason for their most recent business trip was an internal company visit? b. What is the probability that between 18% and 21% of the business travelers say that the reason for their most recent business trip was an internal company visit