8. 7 L of an acid solution was mixed with 3 L of a 15% acid solution to make a 29% acid solution. Find / 3 the percent concentration of the Ent solution. (Must use algebra!)

7 L of one solution is mixed with 3 L of another, making a new solution with a total volume of 10 L and concentration 29%. This means the new solution contains

(10 L) * 29% = (10 L) * 0.29 = 2.9 L

of acid.

Let the concentration of the first solution be c%. Each liter of the 15% acid solution contributes 0.15 L, and each liter of the solution of unknown concentration contributes 0.01c L of acid. To end up with a total of 2.9 L of acid, we would get

7 * (0.01c L) + 3 * (0.15 L) = 2.9 L

Solve for c (we can omit the units):

0.07c + 0.45 = 2.9

0.07c = 2.45

c = 35

So the first solution has a concentration of 35%.

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