Problem 1200

To determine which of the given statements is correct, we need to analyze the information provided and use logical reasoning.

1. Total number of students: 80
2. Number of boys: 40
3. Number of girls: 40
4. Number of students using spectacles: 50

We need to evaluate each statement one by one:

1. Statement 1: Only 10 boys use spectacles
- If only 10 boys use spectacles, then the number of girls using spectacles would be:
$$50 - 10 = 40$$
- This implies all 40 girls use spectacles, which is possible. However, this does not necessarily mean that only 10 boys use spectacles. Therefore, this statement is not necessarily correct.

2. Statement 2: Only 20 girls use spectacles
- If only 20 girls use spectacles, then the number of boys using spectacles would be:
$$50 - 20 = 30$$
- This implies 30 boys use spectacles, which is possible. However, this does not necessarily mean that only 20 girls use spectacles. Therefore, this statement is not necessarily correct.

3. Statement 3: At most 25 boys do not use spectacles
- If at most 25 boys do not use spectacles, then the number of boys using spectacles would be:
$$40 - 25 = 15$$
- This implies at least 15 boys use spectacles. Since the total number of students using spectacles is 50, the number of girls using spectacles would be:
$$50 - 15 = 35$$
- This is possible, but it does not necessarily mean that at most 25 boys do not use spectacles. Therefore, this statement is not necessarily correct.

4. Statement 4: At most 30 girls do not use spectacles
- If at most 30 girls do not use spectacles, then the number of girls using spectacles would be:
$$40 - 30 = 10$$
- This implies at least 10 girls use spectacles. Since the total number of students using spectacles is 50, the number of boys using spectacles would be:
$$50 - 10 = 40$$
- This is possible, and it is consistent with the given information. Therefore, this statement is correct.

Conclusion:
The correct statement is statement 4.

The final answer is "At most 30 girls do not use spectacles."