Q: For the class interval 30-39, what is the class midpoint?

$$\text{Midpoint} = \frac{30 + 39}{2} = 34.5$$

Q: A normal distribution has a mean of 50 and a standard deviation of 5. What range contains approximately 95% of the data?

$$50 \pm 2 \times 5 = 40 \text{ to } 60$$

Question 1

A researcher organizes exam scores into the following classes: 60-69, 70-79, 80-89, 90-99. What is the width of each class?

Accepted Answer

$$	ext{Width} = 10$$

Question 2

Given a class interval of 40-49, what are the upper and lower class limits?

Accepted Answer

Lower: 40, Upper: 49

Question 3

For the class interval 30-39, what is the class midpoint?

Accepted Answer

$$	ext{Midpoint} = \frac{30 + 39}{2} = 34.5$$

Question 4

A frequency distribution has the class interval 50-59. What are the class boundaries?

Accepted Answer

49.5 and 59.5

Question 5

If the frequencies for the classes in a distribution are: 5, 8, 12, 10, what is the cumulative frequency for the third class?

Accepted Answer

$$5 + 8 + 12 = 25$$

Question 6

A class has a frequency of 15 in a dataset of 60 total observations. What is the relative frequency for this class?

Accepted Answer

$$\frac{15}{60} = 0.25$$

Question 7

Which of the following best describes a 'normal' distribution?

Accepted Answer

A distribution that is symmetric and bell-shaped, with most values near the mean.

Question 8

In a normal distribution, approximately what percentage of data falls within one standard deviation of the mean?

Accepted Answer

$$\approx 68\%$$

Question 9

A hospital records the number of patients admitted each day for a week: 12, 15, 18, 20, 22, 25, 30. What is the cumulative frequency for the fifth day?

Accepted Answer

$$12 + 15 + 18 + 20 + 22 = 87$$

Question 10

A frequency distribution has the following classes: 10-19, 20-29, 30-39. What are the boundaries for the second class?

Accepted Answer

19.5 and 29.5

Question 11

If a class interval is 100-109, what is the midpoint?

Accepted Answer

$$\frac{100 + 109}{2} = 104.5$$

Question 12

A dataset has the following frequencies for three classes: 7, 13, 20. What is the relative frequency for the second class?

Accepted Answer

$$\frac{13}{7 + 13 + 20} = \frac{13}{40} = 0.325$$

Question 13

Which of the following statements about class boundaries is correct?

Accepted Answer

Class boundaries are used to avoid gaps between adjacent classes.

Question 14

A normal distribution has a mean of 50 and a standard deviation of 5. What range contains approximately 95% of the data?

Accepted Answer

$$50 \pm 2 	imes 5 = 40 	ext{ to } 60$$

Question 15

A frequency distribution has the following classes: 5-14, 15-24, 25-34. What is the width of each class?

Accepted Answer

$$14 - 5 + 1 = 10$$

Question 16

If a class interval is 200-209, what are the upper and lower class limits?

Accepted Answer

Lower: 200, Upper: 209

Question 17

A dataset has 100 values. If the frequency for a class is 40, what is the relative frequency?

Accepted Answer

$$\frac{40}{100} = 0.40$$

Question 18

Which of the following is NOT a characteristic of a normal distribution?

Accepted Answer

It is skewed to the left.

Question 19

A frequency distribution has the following classes: 1-5, 6-10, 11-15. What is the midpoint of the third class?

Accepted Answer

$$\frac{11 + 15}{2} = 13$$

Introductory Statistics Quiz 2-1 Study Guidance

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