Question

Determine the amounts of 20% and 50% saline solutions that should be mixed to obtain 300 gallons of 42% saline slution

Answer 1

80 gallons of 20%, 220 gallons of 50%. I am very sorry I can't show you the math, I forgot hot to do it so I did it fairly unconventionally.
To prove it's accuracy, multiply 300(gallons) by .42(42%) =126

Then multiply 80(gallons) by .20(20%) = 16
and add it to 220(gallons multiplied by .50(50%) = 110 (16+110=126)
You will come up with the same value.

There is an actual formula to calculate this, it just escapes me right now.