A bag contaions 78 boxes of staple pins of two sizes, large and small. Each large box weighs 10g and each small box weighs 7g. If the total weight of the boxes in the bag is 672g. How many of each type are in the bag?

Answer 1

L + S = 78 ... multiplying by 7 ... 7 L + 7 S = 546

10 L + 7 S = 672

subtracting equations (to eliminate S) ... 3 L = 672 - 546

solve for L , then substitute back to find S