A solution of ‘THANDA SHARBAT’ has 15% sugar. Another solution has 5% sugar. How many liters’ of the second solution must be added to the 20L of first solution to make a solution of 10 % sugar?

Sure, let's solve this step by step:

1. First, let's find out how much sugar is there in the first solution. It has 15% sugar, so in 20L of the solution, the amount of sugar would be 15/100 * 20 = 3L.

2. Let's assume that 'x' liters of the second solution is added to the first solution. The second solution has 5% sugar, so the amount of sugar in 'x' liters would be 5/100 * x = 0.05x L.

3. The total amount of sugar in the new solution is the sum of the sugar in the first and second solutions, which is 3 + 0.05x L.

4. The total volume of the new solution is the sum of the volumes of the first and second solutions, which is 20 + x L.

5. The percentage of sugar in the new solution is the total amount of sugar divided by the total volume, multiplied by 100. So, it is (3 + 0.05x) / (20 + x) * 100.

6. According to the problem, this percentage is 10. So, we can set up the equation: (3 + 0.05x) / (20 + x) * 100 = 10.

7. Simplifying this equation, we get: 3 + 0.05x = 2 + 0.1x.

8. Solving for 'x', we get: x = 20L.

So, 20 liters of the second solution must be added to the 20L of the first solution to make a solution of 10% sugar.