Frequency density = Frequency / Class Width

Class width goes along the x-axis and frequency density goes up the y.

To find the exact value of a bar first use the formula Frequency = Frequency Density x Class Width

Multiply the frequency density of the part of the class you’re interested in.

Example 1:

Estimate the number of beetles between 7.5mm and 12.5mm in length.

Do the frequency density x class width of the first bar, but because it goes up to 10, take away 7.5 and do frequency density x 10-7.5.

For the other bar, it goes ho to 15 and so do 12.5-10 x frequency density.

To find the mean of a histogram, find the midpoint of each class width, multiply that by the frequency and the add all of those values up.

Do this total value divided by the total number of people and you get the mean.

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