A frequency polygon is used to display grouped data

To draw a frequency polygon we plot the midpoint of the group against the frequency and then join the points with straight lines

---

Here is a frequency table showing the time, in minutes, it took for 25 students to get to school one day

Time	Frequency
0 ≤ t ≤ 10	7
10 ≤ t ≤ 20	9
20 ≤ t ≤ 30	6
30 ≤ t ≤ 40	3

To draw a frequency polygon we plot the midpoint with each group against the frequency

The midpoint of 0 and 10 is 5
We could work this out by adding 0 and 10, and then dividing by 2: 0 + 10⁄2 = 5

For the first point we plot (5, 7)

---

The midpoint of 10 and 20 is 15
10 + 20⁄2 = 15

The second point is (15,9)

---

The midpoint of 20 and 30 is 25
20 + 30⁄2 = 25

The next point is (25,6)

---

The midpoint of 30 and 40 is 35
30 + 40⁄2 = 35

The next point is (35,3)

---

And finally we join the points with straight lines