Question 993666
The store manager decides to make 40lbs of blend of coffees that he plans to sell for 10 dollars a lb. He mixes some coffee that sells for 9 dollars a lb with coffee that sells for 12 dollars a lb. How much of each should he use? (Hint- one coffee is x and the other coffee of the rest of the mixture so use 40 - x for the amount)

I already calculated that 40 lbs of coffee costing 10 dollars a lb would be 400 dollars. Now I need help on how to calculate how many pounds adding up to 40lbs. I would use of each that would bring me to 400 dollars total.
Thank you!
<pre>Since you wish to use x for the amount of one of the blends, then we'll make the amount of the $9/lb-blend to mix, be x
Then amount of the $12/lb-blend to mix is: 40 - x
We then get the following equation: 
9x + 12(40 - x) = 40(10)
 9x + 480 - 12x = 400
           - 3x = 400 - 480
           - 3x = - 80
x, or amount of $9/lb-blend to mix = {{{(- 80)/(- 3)}}}, or {{{highlight_green(26&2/3)}}} lbs
Amount of $12/lb-blend to mix: {{{40 - 26&2/3}}}, or {{{highlight_green(13&1/3)}}} lbs