Question

How many pounds of dog food worth $.80 per pound must be mixed with dog food worth $.65 per pound to make a mixture of 60 pounds worth $.70 per pound?

Answer 1

let the amount of the more expensive mix be x pounds
then the amount of the cheaper mix has to be 60-x pounds

.80x + .65(60-x) = .70(60)
times 100 , (I don't like decimals)
80x + 65(60-x) = 70(60)
80x + 3900 - 65x = 4200
15x = 300
x = 20

Use 20 pounds of the expensive kind and
40 pounds of the cheaper