Example

Frequency Polygon

For this example we will use the hottest days data from the Now You Try! activity on frequency tables.

Step 1: Find the midpoints of each class. Recall that midpoints are found by adding the upper and lower boundaries and dividing by 2.

For example:

\[\dfrac{99.5+104.5}{2}=102\]

Temperature Classes Mid-Points Frequencies
99.5-104.5 102 2
104.5-109.5 107 8
109.5-114.5 112 18
114.5-119.5 117 13
119.5-124.5 122 7
124.5-129.5 127 1
129.5-134.5 132 1

Step 2: Draw the \(x\) and \(y\) axes. Label the \(x\) axis with the midpoint of each class, and then use a suitable scale on the \(y\) axis for the frequencies.

label axis frequency polygon example

Step 3: Using the midpoints for the \(x\) values and the frequencies as the \(y\) values, plot the points.

plotting points frequency polygon example

Step 4: Connect adjacent points with line segments.

connect dots frequency polygon example

To see this worked out watch the following video: