Stat Test 1

Which statement best describes a parameter?

D. A parameter is a numerical measure of a population that is almost always unknown and must be estimated.

Which of the following statements is not a property of the normal curve?

D. P(u-o<x<u+0)=.95

Which of the following statements about the sampling distribution of the sample mean is incorrect?

D. The standard deviation of the sampling distribution is o .

Suppose a random variable x, is best described by a normal distribution with u =60 and o=9. Find the z score that corresponds to the value z=96

A 5/3

The thread life of a particular brand of tire is a random variable best described by a normal distribution with a mean of 60,000 miles and a standard deviation of 1300 miles. What is the probability a particular tire of this brand will last longer than 58, 700 miles ?

A. .8413

Use the standard normal distribution to find P (-2.25 < z < 1.25) .

A. .8821

Whats the Z a /2 when a = 0.02?

A. 2.33

The Central Limit Theorem is considered powerful in statics because ________

A. It works for any population distribution provided the sample size is sufficiently large.

Suppose a random variable x is best described by a normal distribution with u= 60 and o =16. Find the z score that corresponds to the value x=0 .

B. -3.75

Use the standard normal distribution to find P(-2.50 < z < 1.50).

B. .9270

Before a new phone system was installed, the amount a company spent on personal calls followed a normal distribution with an average of $900 per month and a standard deviation of $50 per month. Refer to such expenses as PCE's (personal call experiences). Using the distribution above, what is the probability that during a randomly selected month PCE's were $775 and $990.00?

B. .9579

Suppose a random variable x is best described by a normal distribution with u= 60 and o=5 . Find the z score that corresponds to the value x=60.

B. 0

IQ test scores are normally distributed with a mean of 104 and a standard deviation of 17. An individual's IQ score is found to be 115. Find the z score corresponding to this value.

B. 0.65

Find the z a/2 for the given value of a

B. 1.75

For a standard normal random variable, find the probability that z exceeds the value -1.65.

B. 9505

Which of the following does the Central Limit Theorem allow us to disregard when working with the sampling distribution of the sample mean?

B. The shape of the population distribution .

Suppose students' ages followed a skewed right distribution with a mean of 23 years old and a standard deviation of 4 years. If we randomly sampled 200 students, which of the following statements about the sampling distribution of the sample mean age is incorrect?

B. The standard deviation of the sampling distribution is equal to 4 years.

What is the confidence level of the following confidence interval for u ? 2.33

C . 98%

The price of a gallon of milk follows a normal distribution with a mean of $3.20 and a standard deviation of $.10. What proportion of the milk vendors had prices that were less than $3.075 per gallon?

C. 0.1056

The probability distribution shown below describes a population of measurements.

C. 1

Find a value of the standard normal random variable z, called z0, such that P(-z0<z<z0)=.98

C. 2.33

The number of cars running a red light in a day, at a given intersection, possesses a distribution with a mean of 1.7 cars and a standard deviation of 5. The number of cars running the red light was observed on 100 randomly chosen days and the mean numbers of cars calculated. Describe the sampling distribution of the sample mean.

C. Approximately normal with mean =1.7 and a standard deviation =0.5

The average score of all golfers for a particular course has a mean of66 and a standard deviation of 3.5. Suppose 49 golfers played the course today. Find the probability that the average score of the 49 golfers exceeded 67.

D. .0228

Before a new phone system was installed, the amount a company spent on personal calls followed a normal distribution with an average of $500 per month and a standard deviation of $50 per month. Refer to such expenses as PCE's (personal call experiences). Find the probability that a randomly selected month had PCE's below $350.

D. 0013

The Central Limit Theorem is important in statistics because ________

for a large n, It says the sampling distribution of the sample mean is approximately normal, regardless of the population.