Della went to the store to buy 3 pens and 6 notebooks. She spent $20.25. Felipe went to the same store and bought 4 pens and 5 notebooks. He spent $18.75. How much did 1 pen cost?

Question

anonymous · Answer

@texaschic101 @Gabylovesyou

anonymous · Answer

@Michele_Laino

pinklion23 · Answer

@Igreen @AnswerMyQuestions @sleepyjess @inowalst

michele_laino · Answer

If I call with x the cost of 1 pen, and with y the cost of 1 notebook, then the problem is modeled by the subsequent system:

$$\large \left\{ \begin{gathered}
  3x + 6y = 20.25 \hfill \
  4x + 5y = 18.75 \hfill \ 
\end{gathered}  \right.$$
please solve it for x

anonymous · Answer

thank you @Michele_Laino

anonymous · Answer

@Michele_Laino i still dont get it lol

michele_laino · Answer

hint:
you have to solve that system, using, for example the substitution method, namely, you can find  y from the first equation, and then substitute that expression for y, into the second equation. So you can solve that new second equation for x.
For example, we have:
$$y = \frac{{20.25 - 3x}}{6}$$
then I substitute into the second equation:
$$4x + 5 \cdot \frac{{20.25 - 3x}}{6} = 18.75$$
the please, solve that last equation, for x, and you will get the right answer.

michele_laino · Answer

@kylefoster58