Question 842757
you are multiplying x by .7 when you should be multiplying x by 7.
same with y and same with 480.


.7 is 70 cents a pound.
you want 7 dollars a pound which is 7.


when you solved for y, you got y = x + 480.
that should have been y = 480 - x.


let me go through it and you'll see what and where you went wrong.


x + y = 480 is the first equation
7x + 15y = 8(480) is the second equation.


you want to solve by substitution.
start with x + y = 480
subtract x from both sides of this equation to get y = 480 - x
substitute for y in the second equation to get:


7x + (15 * (480 - x)) = (8 * 480)
simplify to get:
7x + (15 * 480) - (15 * x) = (8 * 480)
simplify further to get:
7x + 7200 - 15x = 3840
combine like terms to get"
-8x + 7200 = 3840
subtract 7200 from both sides of this equation to get:
-8x = 3840 - 7200
simplify to get:
-8x = -3360
multiply both sides of this equation by -1 to get:
8x = 3360
divide both sides of this equation by 8 to get:
x = 420


replace x in the equation of x + y = 480 to get 420 + y = 480
subtract 420 from both sides of this equation to get y = 480 - 420 which simplifies to y = 60


you have x = 420 and y = 60
7 * 420 + 15 * 60 = 3840 for 480 pounds of mix.
divide 3840 by 480 to get:
cost per pound for the mix is equal to 8.


numbers check out so the solution is good.


two mistakes that were obvious were:
you used .7 and .8 and .15 rather than 7 and 8 and 15.
you said y = x + 480 when you should have said y = 480 - x


i didn't check the rest out but, if you follow my logic, you should be able to see where else you went wrong, if  you did anything else wrong.