A mixture of water and sucrose is 10% sucrose by weight. How many grams of pure sucrose must be added to a 200-gram sample of this mixture to produce a mixture that is 20% sucrose?

Answer 1

Your original 10%, 200 g mixture has 180 g of water and 20 g of sucrose. Let x be the number of grams of sucrose you need to add. The reqiuorement is

(20 + x)/180 + x) = 0.20

Solve for x

Answer 2

But, aren't we adding the x grams to the original 200 ?

so I would say:
20+x = .2(200+x)
for x = 25