Don't Know How To Set Up This Percent Problem

[SCSmith]

Margaret mixes 50 milliliters of a solution that is 10% HCL with 100 milliters of a solution that is 25% HCL. What percent of the resulting solution is HCL?

 

[zerohour]

50 ml of solution mixed with 100ml of another solution, Thus total quantity is 150 ml.

50 ml of first solution has 10% HCl, that is 5 ml.
100 ml of second solution has 25% HCl, that is 25 ml.
Total HCl is thus 30 ml.

Percentage of HCL in final solution is thus [30/150]*100 = 20%

 

[Unco]

50 ml of solution mixed with 100ml of another solution, Thus total quantity is 150 ml.

50 ml of first solution has 10% HCl, that is 5 ml.
100 ml of second solution has 25% HCl, that is 25 ml.
Total HCl is thus 30 ml.
Whoah!

50mL of first solution has 10% HCl, that is 5 somethings of HCl, where "somethings" is some kind of measure of amount.
100 ml of second solution has 25% HCl, that is 25 somethings of HCl.
Total HCl is 30 somethings.

Percentage of HCL in final solution is thus [30/150]*100 = 20%