Question

7 L of an acid solution was mixed with a 3 L of a 15% acid solution to make a 29% acid solution. find the percent concentration of the first solution
show the work please!

Answer 1

To solve the this sort of problem: Use the percentages and quantities of each solution to find the amount of acid in each. Add the acid quantities and divide by the total volume to get the final concentration. The wrinkle here is that you know the final concentration and need to find one of the original concentrations, but the structure is the same.

N liters of x% solution = N*x liters of acid (x expressed as a number)
M liters of y% solution = M*y liters of acid (y expressed as a number)

(N*x + M*y) (amount of acid)
----------
(N + M) (total solution volume)

gives the concentration of the final solution (expressed as a number). For this problem, you'll need to solve for x given the final concentration.