Question

A person wishes to mix coffee worth nine dollars per pound with coffee worth three dollars per pound to get 240 pounds of a mixture worth five dollars per pound how many pounds of the nine dollars and the three dollar coffee will be needed

Answer 1

$\bf \begin{array}{lccclll} &amount&price&priced\ amount\\ &-----&-----&--------\\ \textit{9 bucks/lb}&x&9&9x\\ \textit{3 bucks/lb}&y&3&3y\\ -----&-----&-----&-------\\ mixture&240&5&1200 \end{array} \\\\\\ \begin{cases} x+y=240\implies \boxed{y}=240-x\\ 9x+3y=1200\\ ----------\\ 9x+3\left( \boxed{240-x} \right)=1200 \end{cases}$

solve for "x".

what about "y"? well, y = 240 - x