A chef is going to use a mixture of two brands of Italian dressing. The first brand contains 8% vinegar, and the second brand contains 13% vinegar. The chef wants to make 270 milliliters of a dressing that is 9% vinegar. How much of each brand should she use

You want to setup an equation that will match the word problem. Let's call the amount of the first brand, F and the amount of the second brand, S.

We want the total mixture to be 310mL so: F + S = 310

Also, you want the total mixture to contain 8% vinegar so: .06F + .11S = .08(310)

Now, we can solve the system of equations using substitution.

F + S = 310

.06F + .11S = .08(310)

F = 310 - S      [solve 1st equation for F]

.06(310 - S) + .11S = .08(310)     [substitute into 2nd equation]

18.6 -.06S +.11S = 24.8

.05S = 6.2

S = 124

F + 124 = 310     [substitute answer for S back into original equation]

F = 186

to make a 310mL mixture that contains 8% vinegar, use 186mL of the first brand and 124mL of the second bran