A sample of milk contains 5% of water. What quantity of pure milk should be added to 10 L of milk sample to reduce this to 2%?

Correct option is B

​Let the amount of pure milk to be added be x liters.

Initially, the sample contains 10 liters of milk with 5% water. Therefore, the amount of water in the original sample is:

$$\frac{5}{100} \times 10 = 0.5 \text{ liters of water}.$$​​
After adding x liters of pure milk, the total amount of milk becomes (10 + x ) liters.
The water content remains the same at 0.5 liters, but the percentage of water should now be 2%.
We set up the equation for the percentage of water in the new mixture:

$$\frac{0.5}{10 + x} \times 100 = 2\\\ \\\frac{0.5}{10 + x} = 0.02\\\ \\0.5 = 0.02 \times (10 + x)\\\ \\0.5 = 0.2 + 0.02x\\\ \\0.02x = 0.5 - 0.2 = 0.3\\\ \\x = \frac{0.3}{0.02} = 15 \text{ liters}.$$​​
Thus, 15 liters of pure milk should be added to reduce the water percentage to 2%.

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