How much water must be added to 1 liter of a 5% saline to get a 2% saline solution

Answer 1

the amount of saline must be the same before and after mixing:

.05(1) + 0(x) = .02(1+x)
.02x = .03
x = 1.5

check:
5% of 1L = .05L saline
2% of 2.5L = .05L saline

or, you can say that since you want 2/5 the concentration, you need 5/2 the original volume, or 2.5L