Solving a percent mixture problem using a system of linear equations

Question

A scientist mixes water (containing no salt) with a solution that contains 55% salt. She wants to obtain 220 ounces of a mixture that is 20% salt. How many ounces of water and how many ounces of the 55% salt solution should she use?

Water:

Salt Soution:

Answer 1

Say x ounces of water and y ounces of the salt solution

Then

x + y = 220

Ounces of salt in this solution = 0.55 y

So we need 0.55 y / 220 = 0.20

So y = 80

x = 140