Question

A​ doctor's prescription calls for a daily intake containing 50 mg of vitamin C and 10 mg of vitamin D. Your pharmacy stocks two compounds that can be​ used: one contains 80% vitamin C and 10% vitamin​ D, the other 40% vitamin C and 20% vitamin D. How many milligrams of each compound should be mixed to fill the​ prescription?

Answer 1

Setup
0.8x + 0.4y = 50
0.1x + 0.2y = 10 - Multiply by -2 and add

get
0.6x = 30
x = 50 mg compound A

.1 (50) + .2y = 10
5 + .2y = 10
.2y = 5
y = 25 mg compound B