Answer:
You will need 275 ml of the 90% solution
Step-by-step explanation:
Let the amount of the 90% alcohol be x
Amount of the 30% alcohol solution = 385 ml
The amount of the mixture = 385 + x
(30% of 385) + (90% of x) = 55% of (385+x)
![\begin{gathered} ((30)/(100)*385)+((90)/(100)* x)=(55)/(100)*(385+x) \\ \\ (0.3*385)+(0.9* x)=0.55(385+x) \\ \\ 115.5+0.9x=211.75+0.55x \\ \\ 0.9x-0.55x=211.75-115.5 \\ \\ 0.35x=96.25 \\ \\ x=(96.25)/(0.35) \\ \\ x=275 \\ \\ \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/vtztr3xd65fkox7p3vkq4q1p6fpnzrh6h3.png)
You will need 275 ml of the 90% solution