How much pure alcohol be added to 400 ml of a 15% solution to make its strength 32%?

Explanation

To solve the problem of how much pure alcohol needs to be added to 400 ml of a 15% alcohol solution to make it a 32% solution, we can follow these steps:

### Step 1: Calculate the initial amount of alcohol in the solution
The initial amount of alcohol in the 400 ml solution can be calculated as follows:

\[ \text{Initial amount of alcohol} = \frac{15}{100} \times 400 = 60 \text{ ml} \]
...