All the first-year students in the computer science (CS) department in a university take both the courses (i) AI and (ii) ML. Students from other departments (non-CS students) can also take one of these two courses, but not both. Students who fail in a course get an F grade; others pass and are awarded A or B or C grades depending on their performance. The following are some additional facts about the number of students who took these two courses this year and the grades they obtained.
1. The numbers of non-CS students who took AI and ML were in the ratio 2 : 5.
2. The number of non-CS students who took either AI or ML was equal to the number of CS students.
3. The numbers of non-CS students who failed in the two courses were the same and their total is equal to the number of CS students who got a C grade in ML.
4. In both the courses, 50% of the students who passed got a B grade. But, while the numbers of students who got A and C grades were the same for AI, they were in the ratio 3 : 2 for ML.
5. No CS student failed in AI, while no non-CS student got an A grade in AI.
6. The numbers of CS students who got A, B and C grades respectively in AI were in the ratio 3 : 5 : 2, while in ML the ratio was 4 : 5 : 2.
7. The ratio of the total number of non-CS students failing in one of the two courses to the number of CS students failing in one of the two courses was 3 : 1.
8. 30 students failed in ML. How many students got A grade in AI?
D
Step-by-Step Solution
Key idea: This is a multi-ratio set integration problem. We define a common variable for the CS students and express all other groups in terms of it, using the failure and grade distribution ratios.
Step 1: Define Variables.
Let Total Non-CS = (since Non-CS AI : Non-CS ML = 2 : 5).
Fact 2: CS Students = Total Non-CS = .
Step 2: Analyze Failures.
Fact 8: Total Fail ML = 30.
Fact 3: Non-CS Fail AI = Non-CS Fail ML. Let this be .
Total Non-CS Fail = .
Fact 3: Total Non-CS Fail = CS Students with C in ML. So, .
Fact 7: Ratio of Total Non-CS Fail to Total CS Fail = 3 : 1.
So, Total CS Fail = .
For this to be an integer, must be a multiple of 3. Let .
Then Total Non-CS Fail = , Total CS Fail = .
Non-CS Fail AI = , Non-CS Fail ML = .
.
Fact 5: No CS student failed in AI. So CS Fail AI = 0.
Therefore, Total CS Fail = CS Fail ML = .
Step 3: Analyze ML Grades.
CS ML Total = .
CS ML Fail = .
CS ML Pass = .
Fact 6: CS ML Grades A:B:C = 4:5:2. Sum of parts = 11.
So CS ML Pass must be divisible by 11. Let .
.
We know .
So .
.
Total CS ML = Pass + Fail = .
So .
Step 4: Solve for .
We know Total Fail ML = 30.
Total Fail ML = Non-CS Fail ML + CS Fail ML = .
So .
Then .
Step 5: Calculate Total AI A grades.
Total CS = .
CS AI Total = 210. CS AI Fail = 0 (Fact 5).
CS AI Pass = 210.
Fact 6: CS AI Grades A:B:C = 3:5:2. Sum of parts = 10.
1 part = .
CS AI A = .
Total Non-CS = 210. Non-CS AI = .
Non-CS AI Fail = .
Non-CS AI Pass = .
Fact 4: 50% of students who passed got a B grade.
Total AI Pass = CS AI Pass + Non-CS AI Pass = .
Total AI Pass B = of .
Total AI Pass A + Total AI Pass C = .
Fact 4: Numbers of students who got A and C grades were the same for AI.
So Total AI Pass A = Total AI Pass C = .
Answer: 63