If Mr. Thomas has a daily fluid restriction of 1200 ml and he consumed 810 ml by lunch, how much fluid can he still have for the day?

To determine how much fluid Mr. Thomas can still have for the day, you start with his total daily fluid restriction of 1200 ml. By lunchtime, he has already consumed 810 ml. The next step is to subtract the amount he has already had from his daily limit.

The calculation would be:

1200 ml (total allowance) - 810 ml (consumed) = 390 ml remaining.

This means that Mr. Thomas can still consume 390 ml for the rest of the day, allowing him to stay within his fluid restriction of 1200 ml. This confirms that the correct answer is indeed the amount he can still drink after accounting for what he has already consumed.