Question

A pharmacist wants to mix a 16% saline solution with a 40% saline solution to get 32 L of a 25%

saline solution. How much of each solution should she use?
A) 12 L of the 16% solution; 20 L of the 40% solution
B) 20 L of the 16% solution; 12 L of the 40% solution
C) 21 L of the 16% solution; 11 L of the 40% solution
D) 11 L of the 16% solution; 21 L of the 40% solution

Answer 1

B) 20 L of the 16% solution; 12 L of the 40% solution

Explanation:

Let the amount of 16% solution = x

the amount of 40% solution = y

[1] the total volume is 32 L

x + y = 32

[2] the concentration is 25%

16% × x + 40% × y = 25% × 32

0.16x + 0.4y = 8

2x + 5y = 100

[1] & [2]

x + y = 32 ⇔ 2x + 2y = 64

2x + 5y = 100 ⇔ 2x + 5y = 100

----------------------- (-)

-3y = -36

y = 12 L

[1]

x + y = 32

x + 12 = 32

x = 20 L