Question

1. The mean clotting time of blood is 7.45 seconds with a standard deviation of 3.6 seconds. What is the probability that an​ individual's clotting time will be less than 7

seconds or greater than 8 ​seconds? Assume a normal distribution. This problem can be solved using technology or the table for the standard normal curve from your text.

2. A teacher gives a test to a large group of students. The results are closely approximated by a normal curve. The mean is

77​, with a standard deviation of 8. The teacher wishes to give​ A's to the top 7​% of the students and​ F's to the bottom

7​%. A grade of B is given to the next 20​%, with​ D's given similarly. All other students get​ C's. Find the bottom cutoff for a grade of C.

3. The chickens at Colonel​ Thompson's Ranch have a mean weight of 1750​g, with a standard deviation of 160g. The weights of the chickens are closely approximated by a normal curve. Find the percent of all chickens having weights more than 2088g or less than 1405g.

4.

Suppose that the life expectancy of a certain brand of non-defective light bulbs is normally​ distributed, with a mean life of

1500 hr and a standard deviation of 150 hr. If 70,000 of these bulbs are​ produced, how many can be expected to last less than 1680

​hr?

Answer 1