SOLUTION: It is desired to draw off a part of 10 gallons of 30% solution of alcohol and to replace it by pure alcohol so as to produce a 50% solution. How many gallons should be drawn off?

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Question 1203496: It is desired to draw off a part of 10 gallons of 30% solution of alcohol and to replace it by pure alcohol so as to produce a 50% solution. How many gallons should be drawn off?
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
Helpful guide here: https://www.algebra.com/my/drain-and-replace-antifreeze.lesson?content_action=show_dev
https://www.algebra.com/my/drain-and-replace-antifreeze.lesson?content_action=show_dev

This method may be approximate, not perfectly accurate:


Draw off some v gallons of the 30% alcohol.
Replace with v gallons of the 100% alcohol.
Want 50% alcohol result.

%2810%2A0.30-0.3v%2Bv%29%2F10=0.50
-
0.3%2A10%2B%281-0.3%29v=10%2A0.5
%281-0.3%29v=10%2A0.5-0.3%2A10
v=%280.5%2A10-0.3%2A10%29%2F%281-0.3%29-----------all computations have been postponed to here.
Now just compute v.