Chapter 13 · Question 1

State the direct method formula for mean of grouped data.

Answer

For grouped data,

\bar{x}=\frac{\sum f_i x_i}{\sum f_i}

, where

x_i

is the class mark and

f_i

is the frequency.

Multiply each class mark by its frequency, add, and divide by total frequency.

For each class, find class mark

x_i=\frac{\text{lower limit}+\text{upper limit}}2

. Then multiply by frequency

f_i

. The mean is

\bar{x}=\frac{\sum f_i x_i}{\sum f_i}

.

For grouped data, $\bar{x}=\frac{\sum f_i x_i}{\sum f_i}$ , where $x_i$ is the class mark and $f_i$ is the frequency.