There are two Classes A and B having 25 and 30 students respectively. In Class-A the highest score is 21 and lowest score is 17. In Class-B the highest score is 30 and lowest score is 22. Four students are shifted from Class-A to Class-B. Consider the following statements: 1. The average score of Class-B will definitely decrease. 2. The average score of Class-A will definitely increase. Which of the above statements is/are correct?

Statement 1: The average score of Class-B will definitely decrease. The lowest score in Class-B is 22. The highest score in Class-A is 21. This means any student shifted from Class-A to Class-B will have a score of at most 21. Since all existing students in Class-B have scores of 22 or higher, any student coming from Class-A will have a score lower than any student already in Class-B. Adding students with scores lower than the current average of Class-B will definitely decrease the average score of Class-B. So, Statement 1 is correct.

Statement 2: The average score of Class-A will definitely increase. Class-A has scores ranging from 17 to 21. When 4 students are shifted out, we don't know which students are removed. If the 4 students with the lowest scores are removed, the average of the remaining students will increase. However, if the 4 students with the highest scores are removed, the average of the remaining students will decrease. Since the specific scores of the shifted students are unknown, we cannot definitively say that the average score of Class-A will increase. So, Statement 2 is not definitely correct.

Therefore, only Statement 1 is correct.

The final answer is A.