We begin with 100 mL of the 2% saline solution, and will add x mL of the 0.5% saline solution. The total volume of the mixture will be (100 + x) mL. The total mass of salt will be:
(100)(2%) + (x)(0.5%) = 2 + 0.005x
This would have to be 0.79% of the total volume:
(100+x)(0.79%) = 0.79 + 0.0079x
Equating:
x = 417.24 mL
The answer is .426 or .43 depending on what you round to. The equation for density is
D=m/v so D= 239.2/92 will give you the answer to your problem.
