**Problem**

In a class experiment, a student needs 5 liters of 6% solution. He found a 4% and a 10% solution in the laboratory. How many liters of each solution should he mix in order to obtain 5 liters of 6% solution?

A. 3.33 liters of 4% and 1.67 liters of 10% solution

B. 1.67 liters of 4% and 3.33 liters of 10% solution

C. 3.67 liters of 4% and 1.33 liters of 10% solution

D. 1.33 liters of 4% and 3.67 liters of 10% solution

**Solution**

Let

x = volume in liters of 4% solution

y = volume in liters of 10% solution

x = volume in liters of 4% solution

y = volume in liters of 10% solution

$x + y = 5$

$y = 5 - x$ ← Equation (1)

$4x + 10y = 6(5)$

$4x + 10(5 - x) = 30$

$4x + 50 - 10x = 30$

$6x = 20$

$x = 3.33 ~ \text{liters}$

From Equation (1)

$y = 5 - 3.33$

$y = 1.67 ~ \text{liters}$

Thus, [ A ] *answer*