Question 193316
let x and y be the amount of 12 and 9 dollar coffee respectively
:
x+y=20...........eq 1
12x+9y=10(20)....eq 2
:
rewrite eq 1 to x=12-y and plug it into eq 2
:
12(20-y)+9y=200
:
240-12y+9y=200
:
-3y=-40
:
y=13.33 pounds of 9 dollar coffee
:
x=20-13.33=6.67 pounds of 12 dollar coffee