Question 2: Hours of sleep (10 points)
A random sample of 8 students at a college reported their hours of sleep last night: 6, 7, 8, 5, 9, 7, 6, 8.
- (a) Find the mean of the 8 values. (2 points)
- (b) Find the sample standard deviation of the 8 values, to one decimal place. (3 points)
- (c) Find the median and the quartiles. Describe the shape of the distribution. (2 points)
- (d) Another student slept 10 hours. Find the z-score of 10 hours using your answers to (a) and (b), and say what it means. (3 points)
Question 3: Biking to work (10 points)
A town says that 30% of its working residents bike to work. In a random sample of 200 working residents, 75 bike to work. Is there convincing evidence, at the 5% level, that more than 30% of the town's working residents bike to work?
- (a) State the hypotheses and say what the parameter is. (2 points)
- (b) Check the conditions for a one-sample z-test for a proportion. (2 points)
- (c) Find the test statistic and the p-value. (4 points)
- (d) State your conclusion in context. (2 points)
Question 4: Checking items at a factory (10 points)
At a factory, each item from a machine needs a second check with probability 0.3, independently of other items. The weights of the items are normal with mean 70 grams and standard deviation 6 grams.
- (a) 8 items are picked. Find the probability that exactly 2 of them need a second check. (3 points)
- (b) For 8 items, find the mean and the standard deviation of the number that need a second check. (2 points)
- (c) Find the probability that one item weighs more than 80 grams. (3 points)
- (d) Two items are picked. Find the probability that both weigh more than 80 grams. What do you have to assume? (2 points)