One solution contains 2 parts salt to 8 parts water, and another contains 3 parts salt to 5 parts water. How much of each should be mixed together in order to obtain 280 quarts of a solution that is 3 parts salt to 7 parts water?

First solution at 2/8 = 25%

second solution at 3/5 = 60%

third the final mixture volume = 280 quarts at 3/7 = 43%

Let x be the volume of the 1st solution salted at 2/8 = 25%

then the 1st solution is 0.25 x

What is missing now is the volume of the second solution, but if we read again the last part we know that the total volume = 280 at 43%

Then volume of B = (280-x) (Since the volume of A + B = 280)

Hence the equation

1st + 2nd = 3rd

25%. x + 60%. (280-x) = 43%.280==> 0.25x + 168 - 0.6 x = 120.4

- 0.35x = - 47.6 = = > 0.35x = 47.6 & x = 136 quart