2

A dentist records the number of cavities in 100 children from a school. The information obtained is summarized in the following table:

No. of cavities fi ni
0 25 0.25
1 20 0.2
2 x z
3 15 0.15
4 y 0.05

1. Complete the table to obtain the values of x, y, z.

2. Create a pie chart.

3. Calculate the average number of cavities.


1. Table

The sum of the relative frequencies must be equal to 1:

0.25 + 0.2 + z + 0.15 + 0.05 = 1

0.65 + z = 1 z = 0.35

The relative frequency of the data equals the absolute frequency divided by 100, which is the sum of the absolute frequencies.

Statistical Exercise

Statistical Problem

No. de caries fi ni fi · ni
0 25 0.25 0
1 20 0.2 20
2 35 0.35 70
3 15 0.15 45
4 5 0.05 20
      155

2. Pie chart

Calculate the degrees corresponding to each absolute frequency.

Statistical Operations

25 · 3.6 = 90º 20 · 3.6 = 72º 35 · 3.6 = 126º

15 · 3.6 = 54º 5 · 3.6 = 18º

Pie Chart


3. Arithmetic Mean

Arithmetic Mean Solution