I've been on this problem for a very long time. I've been trying to translate the problem into a system for elimination but I just can't seem to do it correctly.
A chemist needs 5 liters of a 29% acid solution. He has a 25% solution and a 50% solution available to form the mixture. How much of each should be used to form the 29% solution?
Let amount of 25% solution to mix, be T, and amount of 50%, F
Then, T + F = 5 ----- eq (i)
Also, .25T + .5F = .29(5)____.25T + .5F = 1.45 ------- eq (ii)
- .5T - F = - 2.9 ------ Multiplying eq (ii) by - 2 ------- eq (iii)
Now, just add eqs (iii) & (i) to ELIMINATE F and determine T, the amount of 25% solution to mix.
Substitute the value of T into any of the 1st 2 ORIGINAL equations to determine the value of F, the amount of 50% solution.