9 gal. of a sugar solution was mixed with 6 gal. of a 90% solution to make a 84% sugar solution. Find the percent concentration of the first solution.

Question

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Answer 1

Let x = % of the unknown solution, then

{ (9 gal)(x%) + (6 gal)(90%) }/(9 gal + 6 gal) = 84%

Solving for x we find that the unknown % is 80%