Histograms Quiz

1. What quantity is plotted on the vertical axis of a histogram?

• A. Frequency
• B. Frequency density
• C. Cumulative frequency
• D. Class width

2. A class interval $10 \le t < 20$ has frequency 30. What is its frequency density?

• A. 30
• B. 3.0
• C. 300
• D. 0.3

3. A histogram bar has frequency density 1.2 and spans the class $20 \le t < 40$. What is the frequency for this class?

• A. 1.2
• B. 20
• C. 24
• D. 40

4. Why do histograms use frequency density instead of frequency when class widths are unequal?

• A. Frequency density is always a whole number
• B. So bar area (not height) fairly represents frequency across differently-sized classes
• C. Frequency density is easier to measure with a ruler
• D. Frequency cannot be calculated for continuous data

5. A bar covers $20 \le t < 40$ with frequency density 1.2. Estimate the frequency for the sub-interval $20 \le t < 30$.

• A. 24
• B. 12
• C. 1.2
• D. 6