Please Help… Statistics?

1. A new extended-life light bulb has an average service life of 771 hours, with a standard deviation of 49 hours. If the service life of these light bulbs approximates a normal distribution, about what percent of the distribution will be between 530 hours and 830 hours?
a. 44.285%
b. 79.713%
c. 11.43%
d. 88.57%
2. The distribution of the annual incomes of a group of middle management employees approximated a normal distribution with a mean of $39,186 and a standard deviation of $825. About 74 percent of the incomes lie between what two incomes?
a. $37,254 and $41,118
b. $38,254 and $40,118
c. $37,054 and $41,318
d. $37,454 and $40,918
3. The distribution of the annual incomes of a group of middle management employees approximated a normal distribution with a mean of $39,186 and a standard deviation of $825. About 74 percent of the incomes lie between what two incomes?
a. $37,254 and $41,118
b. $38,254 and $40,118
c. $37,054 and $41,318
d. $37,454 and $40,918
4. A binomial distribution has 96 trials (n = 96) with a probability of success of 0.24 (π=0.24). To apply the normal distribution to approximate the binomial, what are the mean and standard deviation?
a. µ =4.80 and σ = 1.91
b. µ =16.80 and σ = 3.57
c. µ =23.04 and σ = 4.18
d. µ =12.00 and σ = 3.02
5. The average score of 100 students taking a statistics final was 70 with a standard deviation of 7. Assuming a normal distribution, what test score separates the top 25% of the students from the lower 75% of students?
a. 70.00
b. 74.69
c. 65.31
d. 75.25
6.
False
To study the population of consumer perceptions of new technology, sampling of the population is preferred over surveying the population because
a. Sampling is more accurate.
b. We can compute z-scores.
c. It is quicker.
d. Sampling methods are simple.
7. When testing the safety of cars using crash tests, a sample of 1 or 2 cars is used because
a. Sampling is more accurate.
b. Cars are destroyed.
c. It is quicker.
d. The population is very large.
8. When testing the safety of cars using crash tests, a sample of 1 or 2 cars is used because
a. Sampling is more accurate.
b. Cars are destroyed.
c. It is quicker.
d. The population is very large.
9. Recently, a university surveyed recent graduates of the English Department for their starting salaries. Four hundred graduates returned the survey. The average salary was $25,849. The population standard deviation is $2,557. What is the 95% confidence interval for the mean salary of all graduates from the English Department?
a. [$25,598, $26,100]
b. [$25,609, $27,368]
c. [$25,638, $26,060]
d. [$25,519, $26,179]
10. A survey of 45 retail stores revealed that the average price of a microwave was $390 with a standard error of $25. Assuming the population is normally distributed, what is the 95% confidence interval to estimate the true cost of the microwave?
a. $382.99 to $397.01
b. $382.70 to $397.30
c. $385.23 to $394.77
d. $383.85 to $396.15
11. A survey of 21 grocery stores revealed that the average price of a gallon of milk was $2.67 with a standard error of $0.50. What is the 95% confidence interval to estimate the true cost of a gallon of milk?
a. $2.46 to $2.49
b. $3.50 to $2.88
c. $1.85 to $2.85
d. $1.63 to $3.71
12. A pharmaceutical company wanted to estimate the population mean of monthly sales for their 250 sales people. 45 sales people were randomly selected. Their mean monthly sales was $10,309 with a population standard deviation of $1,032. Construct a 95% confidence interval for the population mean.
a. [10,112.1, 10,505.9]
b. [10,019.8, 10,598.2]
c. [10,055.2, 10,562.8]
d. [10,007.5, 10,610.5]

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