Math Help for Section 3.2, Page 113

Study
Tip:
The average
of a set of values is defined as the sum of the values divided by the
number of values.

Example
4: Check

    $\eqalign{{{87 + 92 + 84 + x} \over 4}
=&
90&{\small\color{red}\quad\quad\text{Write original
equation.}}  \cr {{87 + 92 + 84 + \color{red}97\color{black}}
\over 4} \overset{?}{=}&
90&{\small\color{red}\quad\quad\text{Substitute 97 for }x.}  \cr {{360} \over
4} \overset{?}{=}&
90&{\small\color{red}\quad\quad\text{Add.}} \cr 90 =& 90&{\small\color{red}\quad\quad\text{Solution
checks. }\checkmark} \cr} $