Correct option is D

Solution:
For the year 2020:
Total students in 2020 = 1200 (A) + 900 (B) + 1000 (C) + 700 (D) = 3800
For the year 2023:
Total students in 2023 = 600 (A) + 700 (B) + 800 (C) + 1000 (D) = 3100
The difference between the number of students enrolled in 2020 and 2023 = 3800 - 3100 = 700
Hence, the total number of students enrolled in the year 2020 is 700 more than the total number of students enrolled in the year 2023.

Correct option is B

Given:
Number of students in College B in 2021 = 800
Number of students in College C in 2022 = 1200
Ratio of girls to boys in College B (2021) = 3:5
Ratio of girls to boys in College C (2022) = 7:5
Solution:
Total students in College B in 2021 = 800
Ratio of girls to boys = 3:5
Total parts = 3 + 5 = 8 parts
Number of girls in College B = $$\frac 38$$​ × 800 = 300 girls

Number of boys in College B = $$\frac 58 \times$$ 800 = 500 boys
Total students in College C in 2022 = 1200
Ratio of girls to boys = 7:5
Total parts = 7 + 5 = 12 parts
Number of girls in College C  =$$\frac{7}{12}$$​ × 100 = 700 girls

Number of boys in College C = $$\frac 5 {12}$$​ × 1200 = 500 boys
Ratio between the number of girls in College B (2021) to the number of boys in College C (2022) = 300: 500 = 3: 5

Correct option is D

Given:
Total number of students in College B in 2021 = 800
20% of students were enrolled in B.Sc
30% of students were enrolled in B.Com
The remaining students were enrolled in BCA
Solution:
Number of students in B.Sc = 20% of 800 = 0.20 × 800 = 160 students
Number of students in B.Com = 30% of 800 = 0.30 × 800 = 240 students
Number of students in BCA = Remaining students = 50% of 800 = 0.50 × 800 = 400 students
Difference between the number of students enrolled in BCA and B.Sc = 400 (BCA) - 160 (B.Sc) = 240 students
Hence, the difference between the number of students enrolled in BCA and B.Sc is 240 students.

Correct option is A

Given:
Number of students enrolled in College B:
2020: 900 students
2021: 800 students
2022: 1000 students
2023: 700 students
Solution:
Total number of students in College B = 900 + 800 + 1000 + 700 = 3400 students
Average number of students = $$\frac{\text{Total number of students}}{\text{Number of years}}$$​​
Average = $$\frac{3400}{4} = 850 \, \text{students}$$​​
Hence, the average number of students enrolled in College B over the four years is 850 students.

Correct option is D

Given:
Number of students in College A:
2020: 1200 students
2021: 1100 students
Number of students in College C:
2022: 1200 students
2023: 800 students 
Solution:
Total for College C = 1200 + 800 = 2000 students
Total for College A = 1200 + 1100 = 2300 students
Percentage increase in students = $$\left( \frac{\text{Total for College A} - \text{Total for College C}}{\text{Total for College C}} \right) \times 100$$​​
Percentage increase = $$\left( \frac{2300 - 2000}{2000} \right) \times 100 = 15\%$$​​
Hence, the number of students enrolled in College A (2020 and 2021) is 15% more than the number of students enrolled in College C (2022 and 2023).