TEST 4
1.
The management of KSmall Industries is considering a new method of assembling a computer.
The current assembling method requires a mean time of 120 minutes with a standard deviation
of 4.7 minutes. Using the new method, the mean assembly time for a random sample of 44
computers was 38 minutes. Using the .01 level of significance, can we that the assembly time
using the new method is faster?
2.
A recent national survey found that high school students watched an average (mean) of 6.8
movies per month with a population standard deviation of 0.8. The distribution of the number of
movies watched per month follows the normal distribution. A random sample of 32 college
students revealed that the mean number of movies watched last month was 4.2. At the .07
significance level, can we conclude that college students watch fewer movies a month than high
school students?
3.
The mean income per person in the United States is $66,000, and the distribution of incomes
follows a normal distribution. A random sample of 13 residents of Wilmington, Delaware, had a
mean of $72,000 with a standard deviation of $10,500. At the .03 level of significance, is that
enough evidence to conclude that residents of Wilmington, Delaware, have more income than
the national average?
4.
The average cost of tuition plus room and board for a small private liberal arts college is reported
to be $3,800 per term, but a financial administrator believes that the average cost is higher. A
study conducted using 350 small liberal arts colleges showed that the average cost per term is
$7,645. The population standard deviation is $1,234. Let α = 0.04. What is the critical z-value for
this test?
