We can solve this problem by setting up a proportion. When creating the proportion it is important to keep the units aligned. Our proportion would look like this:
We are looking for x, the amount of sugar she needs with 40% sugar syrup. To solve, we can cross multiply and divide. We cross multiply 10 x 40, then divide by 25:
10 x 40 = 400
400/25 = 16
Ms. Maryna needs 16 lbs of sugar to make 40% sugar syrup.