A 40 -litre mixture contains 25% alcohol and 75% water. If 10 litres of water are added to the mixture, the percentage of alcohol in the new mixture is:

Initial volume of the mixture = 40 litres 

Initial percentage of alcohol = 25%   

Initial percentage of water = 75%   

10 litres of water are added to the mixture.  

​$$\text{Percentage of alcohol} = \frac{\text{Amount of alcohol in litres}}{\text{New total volume of the mixture}} \times 100$$