To create a 9% vinegar mixture, the chef should use 192 milliliters of the first brand (7% vinegar) and 128 milliliters of the second brand (12% vinegar).
The student is asking how to mix two brands of Italian dressing to create 320 milliliters of dressing with a 9% vinegar concentration. One brand has 7% vinegar, and the other has 12% vinegar.
To solve this, we let x be the amount of the first brand (7% vinegar) and 320 - x be the amount of the second brand (12% vinegar). The total amount of vinegar from both brands should equal 9% of the total solution (320 milliliters).
We can set up the equation: 0.07x + 0.12(320 - x) = 0.09 \( 320 \) and solve for x.
Multiplying out the terms gives us:
0.07x + 38.4 - 0.12x = 28.8
Combining like terms gives us:
-0.05x + 38.4 = 28.8
Solving for x, we find:
x = (38.4 - 28.8) / 0.05
x = 192 milliliters of the first brand and 320 - 192 = 128 milliliters of the second brand.