Alex weighs 85 pounds. Together, he and his weigh ten pounds more than five times the weight of his siter. What is the weight , w, of alex's sister?
Let w be the weight of Alex's sister.
The total weight of Alex and his sister is w + 85 pounds.
Five times the weight of his sister is 5w pounds.
w + 85 = 5w + 10 pounds.
Combine like terms: w - 5w = 10 - 85
-4w = -75
Divide both sides by -4: w = -75 / -4
w = <<75/4=18.75>>18.75 pounds. Answer: \boxed{18.75}.