A grocer has two kinds of candies: one sells for 90 cents per pound and the other sells for 40 cents per pound. How many pounds of each kind must he use to make 50
pounds he can sell for 85 cents per pound?

Given:

Candy x = 0.90 per pound  

Candy y = 0.40 per pound

100 pounds * 0.85 per pound = 85

x + y = 100

0.90x + 0.40y = 85

x = 100 - y

0.90(100 - y) + 0.40y = 85

90 - 0.90y + 0.40y = 85

-0.50y = 85 - 90

y = -5 / -0.50

y = 10

x = 100 - y

x = 100 - 10

x = 90

0.90x + 0.40y = 85

0.90(90) + 0.40(10) = 85

81 + 4 = 85

85 = 85