Respuesta :
Assuming these are volume percentages and the volumes don't change when you mix them, we can calculate this using a system of equations.
But first we need to identify each equation and variable.
let x be the volume of 7% vinegar used and y be the volume of 12% vinegar used.
The total volume is the sum of those and it must be equal to 370 mL, so:
[tex]x+y=370[/tex]The amount of vinegar in the x volume of 7% vinegar can be calculated by multiplying x by the 7%, that is, by 0.07:
[tex]0.07x[/tex]Similarly, the amount of vinegar in y is:
[tex]0.12y[/tex]So, the total amount of vinegar after the mixture is:
[tex]0.07x+0.12y[/tex]Since the percentage of the final mixture is 8%, the amount after the mixture can also be calculated by taking 8% of the final volume of 370mL, that is:
[tex]0.08\cdot370=29.6[/tex]The two ways of calculating the amount of vinegar in the mixture must be the same, so we have got our second equation:
[tex]0.07x+0.12y=29.6[/tex]So, the system of equations is:
[tex]\begin{gathered} x+y=370 \\ 0.07x+0.12=29.6 \end{gathered}[/tex]We can solve this by substitution:
[tex]\begin{gathered} x+y=370 \\ x=370-y \end{gathered}[/tex]Thus:
[tex]\begin{gathered} 0.07x+0.12y=29.6 \\ 0.07(370-y)+0.12y=29.6 \\ 0.07\cdot370-0.07y+0.12y=29.6 \\ 25.9+0.05y=29.6 \\ 0.05y=29.6-25.9 \\ 0.05y=3.7 \\ y=\frac{3.7}{0.05} \\ y=74 \end{gathered}[/tex]And, going back to the first equation:
[tex]\begin{gathered} x=370-y \\ x=370-74 \\ x=296 \end{gathered}[/tex]