QZ wrote:

If Amberly wants to create a 40% saline solution combining solution A, which is an 18% saline solution and solution B, which is a 72% saline solution, what must the ratio of the volumes of solution A to solution B be to create a 40% saline solution?

a. 1/2

b. 11/16

c. 3/4

d. 1

e. 16/11

Expanding just a bit on

Leo8 's good post above.

When asked for a ratio of two solutions in a resultant mixture, you can use two variables and simply find their amounts in relation to one another.

One iteration of a weighted average equation here is

(Concentration of A)(Vol A) + (Concen of B)(Vol B) = (Desired Concen)(Total vol = A+B)

"Concentration" here = percent saline

A = the 18% saline solution

B = the 72% saline solution

A + B = total volume of resultant solution

Desired concentration of saline in resultant solution is 40%

.18(A) + .72(B) = .40(A + B)

18A + 72B = 40A + 40B

32B = 22A

Ratio of A to B?

\(\frac{A}{B} = \frac{32}{22}=\frac{16}{11}\), or

16 : 11

Answer E

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