A barrel contains 40 gallons of 30% antifreeze. How many gallons of a 90% antifreeze solution should be added to make the barrel contain 40% antifreeze ?

Answer 1

Use a weighted average expression on these type of problems. Let x = the unknown quanity, then

{ 40(30 + x(90%) }/(40 + x) = 40%

Then;

1200 + 90x = 1600 + 40x or 50x = 400 or x = 8 gallons