A scientist has saline solutions with concentrations of 4% and 14%. He wants to mix some of each solution to get 65 milliliters of solution with a 6% concentration. How many milliliter of each solution does he need to mix together?

Let volume of 4% solution = x and of 14% be y

them x + y = 65 ... (1) also using the actual weights of salt:-

0.04x + 0.14y = 65*0.06 = 3.9

multiplying the above equation by - 25 we have

-x - 3.5y = - 97.5 adding this to equation (1)

--2.5y = - 32.5

y = 13

and x = 65 - 13 = 52

so we need 13 mls of the 14%, and 52 mls of the 4% solution.