Question

Gigi wants to sell 18 kilograms of a cookie mix for $7 a kilogram. She starts with a $5 cookie mix and a $10 cookie mix. How many kilograms of each does she need to make the final mix?
Reiny
amount of cheaper mix --- x kg
amount of expensive mix -- 18-x

solve for x and sub into my definitions

5x + 10(18-x) = 7(18)