Question

A textbook store sold a combined total of 260 chemistry and physics textbooks in a week. The number of chemistry books sold was three times the number of physics textbooks sold. How many textbooks of each type were sold?

Answer 1

Let:

x = Chemistry textbooks sold

y = Physics textbooks sold

The textbook store sold a combined total of 260, so:

$x+y=260$

The number of chemistry books sold was three times the number of physics textbooks sold, so:

$x=3y$

Let:

$\begin{gathered} x+y=260_{\text{ }}(1) \\ x=3y_{\text{ }}(2) \end{gathered}$

Replace (2) into (1):

$\begin{gathered} 3y+y=260 \\ 4y=260 \\ y=\frac{260}{4} \\ y=65 \end{gathered}$

Replace the value of y into (2):

$\begin{gathered} x=3(65) \\ x=195 \end{gathered}$