Correct Answer - Option 4 : 50%

**Given :**

There is a 50 litres solution of alcohol and water

There is 40% alcohol in solution

**Calculation :**

According to the question

Concentration of alcohol in the solution = 40%

Concentration of water = 100 - 40 = 60%

Amount of alcohol = 40% of 50 = 20 litres

Amount of Water = 60% of 50 = 30

Now 10 litres of alcohol is added so,

New amount of alcohol = 20 + 10 = 30 litres

Amount of new mixture = 30 + 30 = 60 litres

Percentage of water in new mixture = (30/60) × 100

⇒ 50%

**∴ Concentration of water in the final mixture will be 50% **