Answer: There is 162 ml of first brand and 108 ml of second brand.
Step-by-step explanation:
Since we have given that
Percentage of vinegar that the first brand contains = 7%
Percentage of vinegar that the second brand contains = 12%
Percentage of vinegar in mixture = 9%
Total amount of dressing = 270 ml
We will use "Mixture and Allegation":
First brand Second brand
7% 12%
9%
--------------------------------------------------------
12%-9% : 9%-7%
3% : 2%
So, ratio of first brand to second brand in a mixture is 3:2.
So, Amount of first brand she should use is given by
[tex]\dfrac{3}{5}\times 270\\\\=162\ ml[/tex]
Amount of second brand she should use is given by
[tex]\dfrac{2}{5}\times 270\\\\=108\ ml[/tex]
Hence, there is 162 ml of first brand and 108 ml of second brand.