Basic Stat HW Ch 7

1

Practice Questions Chapter 7

1.

The number of calories in a salad on the lunch menu is normally distributed with mean 200 and standard

deviation 5.

A

random sample of

16 salads

is selected

.

a.

What is the standard error for the sample mean?

b.

What is

the probability that the

sample

mean is

between

198

and

201

calories

?

2.

Assume that the

amount

of

sugar in a can of soft drink

has a

normal

distribution with a mean of

5

0 grams

and a

standard deviation

of 1

0

. A random sample of 25

cans

is

taken

.

a.

W

hat is the standard error for the sample

mean?

b.

What is the probability that the sample mean

for sugar

is between

48

and

52

grams?

c.

What is the probability that the sample mean for sugar is

exactly 53

grams?

3.

The number of calories in a salad on the lunch menu is

normally

distributed with mean

23

0

and standard

deviation

2

0

.

A

random sample of

16

salads

is selected

.

a.

What is the

standard error for the sample mean?

b.

What is

the probability that the

sample

mean is

more than

2

?

4.

Every year,

t

esters take the Law School Admission Test (LSAT). One year, the scores had a mean

of

150

and

a standard deviation of 9

points,

respectively.

Suppose that in the scoring process, test officials audit

random samples of

36

tests.

a.

What is the standard error

of the

mean?

b.

What is the probability that the sample mean

scores of the test

is

between 1

48.5

and

1

53

?

5.

The weights of

newborn babies

are

normally distributed with a mean of

3.05

kg

and a standard deviation

of 0.

45

kg

. A random sample of

25 newborn babies

is

selected.

a.

What is the standard error for the sample mean?

b.

What is the probability that the sample mean weight of

babies

is less than

2.80

kg

?

6.

The

average

of

text messages

per da

y

is

100

and

the population

standard deviation

is

20

text messages.

Suppose a random sample

of 49 students

is taken.

a.

F

ind

the standard

error

?

b.

What is the probability that the

sample mean is between 95 and 105 messages?

7.

The amount of time necessary for assembly line workers to complete a product is a

normal

random

variable with a mean of 15 minutes and a standard deviation of 8 minutes. A random

sample

of 16 workers

is selected.

a.

What is the probability that t

he sample mean of assembly time is exactly 20 minutes?

b.

What is the probability that the sample mean of assembly time is between 18 and 22 minutes?

1

Practice Questions Chapter 7

1. The number of calories in a salad on the lunch menu is normally distributed with mean 200 and standard

deviation 5. A random sample of 16 salads is selected.

a. What is the standard error for the sample mean?

b. What is the probability that the sample mean is between 198 and 201 calories?

2. Assume that the amount of sugar in a can of soft drink has a normal distribution with a mean of 50 grams

and a standard deviation of 10. A random sample of 25 cans is taken.

a. What is the standard error for the sample mean?

b. What is the probability that the sample mean for sugar is between 48 and 52 grams?

c. What is the probability that the sample mean for sugar is exactly 53 grams?

3. The number of calories in a salad on the lunch menu is normally distributed with mean 230 and standard

deviation 20. A random sample of 16 salads is selected.

a. What is the standard error for the sample mean?

b. What is the probability that the sample mean is more than 2?

4. Every year, testers take the Law School Admission Test (LSAT). One year, the scores had a mean of 150

and a standard deviation of 9 points, respectively. Suppose that in the scoring process, test officials audit

random samples of 36 tests.

a. What is the standard error of the mean?

b. What is the probability that the sample mean scores of the test is between 148.5 and 153?

5. The weights of newborn babies are normally distributed with a mean of 3.05 kg and a standard deviation

of 0.45 kg. A random sample of 25 newborn babies is selected.

a. What is the standard error for the sample mean?

b. What is the probability that the sample mean weight of babies is less than 2.80 kg?

6. The average of text messages per day is 100 and the population standard deviation is 20 text messages.

Suppose a random sample of 49 students is taken.

a. Find the standard error?

b. What is the probability that the sample mean is between 95 and 105 messages?

7. The amount of time necessary for assembly line workers to complete a product is a normal random

variable with a mean of 15 minutes and a standard deviation of 8 minutes. A random sample of 16 workers

is selected.

a. What is the probability that the sample mean of assembly time is exactly 20 minutes?

b. What is the probability that the sample mean of assembly time is between 18 and 22 minutes?