
Solution concentrations
Probably something very simple but can't remember how to do it.
Have a base that is 636.
When solution A is added, it becomes 474.
When solution B is added, it becomes 575.
Now that was a one or the other mix... If I were to mix solution A, B, and the base, then what do I get? How do I get it also..

636 + A = 474
636 + B = 575
Do you see where to go from here?

I get something like this.
636 + A = 474
A = 162
636 + B = 575
B = 61
636 + A + B = 413
But 413 just doesn't seem right.

Perhaps it would help if you stated the whole problem. You titled this "Solution Concentration" and talk about a "mix" but simply adding and subtracting numbers does not appear to me to have any thing to do with mixing.

Ok this is a lubricity chart for diesel fuel. It shows the fuel as having a base of 636, the lower the number, the better the lubricity. The whole chart is based on 35 gallons of fuel, with a certain concentration of additive (solutions A and B) added and then measuring the lubricity. So after solution A was added, the score was 575, after solution B was added, the score was 474. So I want to know what the score would be if solution A and B were added to the fuel at the same time.

It looks to me that you did it correctly. I think what may be throwing you of is the fact that the variables are negative. Remember that the additives are supposed to reduce the score, so that makes perfect sense. Unless I'm missing something, you have it.