As the original average volume of 60 mineral water bottles is 800 ml , we get the total volume as $$60 \times 800=48,000 \mathrm{ml}$$



Now, let the number of 1 liter i.e. 1000 ml water bottles to be removed to reduced the average volume of the remaining bottles as 600 mI be ' n '

We get $$\frac{48000-n \times 1000}{60-n}=600$$ which when simplified gives $$1000 \mathrm{n}-600 \mathrm{n}=48000-36000$ $\Rightarrow \mathrm{n}=\frac{12000}{400}=30$$

Hence 30 water bottles of 1 liter capacity are to be removed to reduce the average to 600 mI . so the answer is (D).