Question 1197162
<font color=black size=3>
You require 1040 mL of a 20% alcohol solution.
That means you need 0.20*1040 = 208 mL of pure alcohol.


x = amount of the 15% solution (in mL)
15% of x = 0.15x = amount of pure alcohol from the 15% solution


1040-x = amount of the 95% solution
note that x and 1040-x combine to 1040


95% of (1040-x) = 0.95(1040-x) = amount of pure alcohol from the 95% solution


Combine the subtotal amounts of pure alcohol from the two batches.
The goal is to get 208 mL of pure alcohol.


0.15x + 0.95(1040-x) = 208
0.15x + 0.95(1040)+0.95(-x) = 208
0.15x + 988 - 0.95x = 208
-0.80x + 988 = 208
-0.80x = 208 - 988
-0.80x = -780
x = -780/(-0.80)
x = 975
You'll need <font color=red>975 mL</font> of the 15% solution


And you'll need 1040-x = 1040-975 = <font color=red>65 mL</font> of the 95% solution.
</font>