In a histogram, the area of each bar shows the frequency, not its height. The height is frequency density = frequency ÷ class width. This lets classes of different widths be compared fairly.
To find a frequency from a histogram, multiply the frequency density by the class width. To estimate how many values fall in part of a class, take the matching fraction of the bar. The total frequency is the total area of all the bars.
Worked example
A bar from 50 to 80 has frequency density 1.2. Find the frequency.
- Class width: 80 − 50 = 30.
- Frequency = 1.2 × 30.
Answer:36
Key words
- frequency density
- frequency ÷ class width
- class width
- the size of the interval
- area
- represents frequency in a histogram
Practise this
New questions every time.
Common Core-referenced: HSS-ID.A.1