How much water must be added to $10\%$ of $350\text{mL}$ alcohol to dilute it to $5\%$

Question

You have $350$ml of cider, with a $10\%$ alcohol content. If you want to dilute the drink to end up with a $5\%$ alcohol content, how much water would you need to add?

Answer 1

Hint: Let $x$ be the amount in ml to be added to the drink, then: $0.05(350+x) = 0.1(350)$

Answer 2

If you want an equation, then the answer by Kf-Sansoo should be all you need.

I'll give you a solution that's easier to follow if you aren't used to setting up equation. This way of solving it is slower, but maybe easier on the intuition.

Just fill in the blanks:

• I have 350mL of 10% cider which measn I have __ mL of pure alcohol.
• I want a 5% alcohol content, which is $\frac1{20}$, so if I have __mL of alcohol, the total volume of the drink must be __mL
• I now have 350mL of the drink, I need __mL, so I need to add __mL more water.