Question

Ms. Adams needs to make 50 ml of 15% saline solution. However, she only has bottles of 7.5% and 20% solution. How many milliliters of each does she need to mix?

Answer 1

Answer: 20 mL of 7.5% solution and 30 mL of 20% solution

Explanation:

Let the amount of 7.5% solution in mL be
`x` and the amount of 20% solution in mL be
`y`.

Then, we know that
`x+y=50` (from the total amount) and that
`0.075x+0.20y=50(0.15)` from the concentration.

`x+y=50 \implies y=50-x\\\\\therefore 0.075x+0.20(50-x)=50(0.15)\\\\0.075x+10-0.20x=7.5\\\\-0.125x=-2.5\\\\x=20\\\\\implies y=50-20=30`