6.2 Mode and Mean of Grouped Data (Examples)

Example:

The following frequency table shows the number of magazines sold at a bookshop for 30 days in April 2013.

Based on the data given,
(a) calculate the size of class,

(b) state the modal class,

(c) calculate the mean number of magazine sold per day.

Solution:

(a) Size of the class

= upper boundary – lower boundary

= 229.5 – 219.5

= 10

(b) Modal class = 240 – 249 (Highest frequency)

(c)

\begin{array}{l} Midpoint = \frac{220 + 229}{2} = 224.5 \\ mean, \bar{x} = \frac{\sum f x}{\sum f} \\ = \frac{3 \times 224.5 + 5 \times 234.5 + 11 \times 244.5 + 6 \times 254.5 + 5 \times 264.5}{30} \\ = \frac{7385}{30} \\ = 246.2 \end{array}