Statistics Examples

$\begin{array}{c} Class & Frequency \\ 19.55 - 21.82 & 3 \\ 21.83 - 24.1 & 5 \\ 24.11 - 26.38 & 9 \\ 26.39 - 28.66 & 6 \\ 28.67 - 30.94 & 2 \end{array}$

Step 1

Find the midpoint $M$ for each class.

$\begin{array}{c} Class & Frequency (f) & Midpoint (M) \\ 19.55 - 21.82 & 3 & 20.685 \\ 21.83 - 24.1 & 5 & 22.965 \\ 24.11 - 26.38 & 9 & 25.245 \\ 26.39 - 28.66 & 6 & 27.525 \\ 28.67 - 30.94 & 2 & 29.805 \end{array}$

Step 2

Multiply the frequency of each class by the class midpoint.

$\begin{array}{c} Class & Frequency (f) & Midpoint (M) & f \cdot M \\ 19.55 - 21.82 & 3 & 20.685 & 3 \cdot 20.685 \\ 21.83 - 24.1 & 5 & 22.965 & 5 \cdot 22.965 \\ 24.11 - 26.38 & 9 & 25.245 & 9 \cdot 25.245 \\ 26.39 - 28.66 & 6 & 27.525 & 6 \cdot 27.525 \\ 28.67 - 30.94 & 2 & 29.805 & 2 \cdot 29.805 \end{array}$

Step 3

Simplify the $f \cdot M$ column.

$\begin{array}{c} Class & Frequency (f) & Midpoint (M) & f \cdot M \\ 19.55 - 21.82 & 3 & 20.685 & 62.054\overline{9} \\ 21.83 - 24.1 & 5 & 22.965 & 114.825 \\ 24.11 - 26.38 & 9 & 25.245 & 227.205 \\ 26.39 - 28.66 & 6 & 27.525 & 165.14\overline{9} \\ 28.67 - 30.94 & 2 & 29.805 & 59.61 \end{array}$

Step 4

Add the values in the $f \cdot M$ column.

$62.054\overline{9} + 114.825 + 227.205 + 165.14\overline{9} + 59.61 = 628.845$

Step 5

Add the values in the frequency column.

$n = 3 + 5 + 9 + 6 + 2 = 25$

Step 6

The mean (mu) is the sum of $f \cdot M$ divided by $n$ , which is the sum of frequencies.

$μ = \frac{\sum_{}^{} f \cdot M}{\sum_{}^{} f}$

Step 7

The mean is the sum of the product of the midpoints and frequencies divided by the total of frequencies.

$μ = \frac{628.845}{25}$

Step 8

Simplify the right side of $μ = \frac{628.845}{25}$ .

$25.1538$