Let X = ml's of 3% hydrochloric acid and Y = ml's of 10% hydrochloric acid
Add X and Y to get the total milliliters:
X + Y = 175
Now multiply the quantities by their percentages go get the 6% required:
0.03x + 0.10y = 0.06(175)
Rewrite the first equation as x = 175 -y
Now replace x in the second equation and solve:
0.03(175-y) + 0.10y = 0.06(175)
Simplify:
5.25 - 0.03y + 0.10y = 10.5
Combine like terms:
5.25 +0.07y = 10.5
Subtract 5.25 from both sides:
0.07y = 5.25
Divide both sides by 0.07:
y = 5.25 / 0.07
y = 75
Now you have y solve for x:
x = 175-y = 175 - 75 = 100
You need 100 ml's of the 3% solution and 75 ml's of the 10% solution.
