Intermediate Algebra, Chapter 2, 2.1, Section 2.1, Problem 64
Evaluate the equation $\displaystyle 0.09x + 0.13 (x + 300) = 61$ and check your solution. $ \begin{equation} \begin{aligned} 0.09x + 0.13 (x + 300) =& 61 && \text{Given equation} \\ 100 [0.09x + 0.13(x + 300)] =& 61(100) && \text{Multiply each term by $100$} \\ 9x + 13(x +300) =& 6100 && \text{Distributive property} \\ 9x + 13x + 3900 =& 6100 && \text{Distributive property} \\ 22x + 3900 =& 6100 && \text{Combine like terms} \\ 22x =& 6100 - 3900 && \text{Subtract $3900$ from each side} \\ 22x =& 2200 && \text{Combine like terms} \\ \frac{22x}{22} =& \frac{2200}{22} && \text{Divide both sides by $22$} \\ x =& 100 && \end{aligned} \end{equation} $ Checking: $ \begin{equation} \begin{aligned} 0.09(100) + 0.13(100 + 300) =& 61 && \text{Let } x = 100 \\ 9 + 52 =& 61 && \text{Multiply} \\ 61 =& 61 && \text{True} \end{aligned} \end{equation} $