A student obtain 75%, 80% and 85% marks in three subjects. If the marks of another subject are added, then his average cannot be less than

Options

A. `60%`
B. `65 %`
C. `80%`
D. `90% `

Answer

To find the minimum average percentage that a student can achieve after adding marks from a fourth subject, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Marks Obtained in Three Subjects:**
- The student has obtained:
- Subject 1: 75%
- Subject 2: 80%
- Subject 3: 85%

2. **Assume Total Marks for Each Subject:**
- Let’s assume that each subject is out of 100 marks. Therefore, the total marks for three subjects = 100 + 100 + 100 = 300.

3. **Calculate the Marks Obtained in Each Subject:**
- Marks obtained in Subject 1 = 75% of 100 = 75 marks
- Marks obtained in Subject 2 = 80% of 100 = 80 marks
- Marks obtained in Subject 3 = 85% of 100 = 85 marks

4. **Calculate Total Marks Obtained in Three Subjects:**
- Total marks obtained = 75 + 80 + 85 = 240 marks.

5. **Consider the Fourth Subject:**
- Let the marks obtained in the fourth subject be 0 (to find the minimum average).
- Total marks for the fourth subject = 100.

6. **Calculate the Total Marks After Adding the Fourth Subject:**
- Total marks after adding the fourth subject = 240 (from the first three subjects) + 0 (from the fourth subject) = 240 marks.

7. **Calculate the Total Number of Subjects:**
- Total number of subjects = 4.

8. **Calculate the Average Marks:**
- Average marks = Total marks obtained / Total number of subjects
- Average marks = 240 / 4 = 60 marks.

9. **Convert the Average Marks to Percentage:**
- Since each subject is out of 100, the average percentage = (Average marks / Total marks per subject) × 100
- Average percentage = (60 / 100) × 100 = 60%.

### Conclusion:
The minimum average percentage that the student can achieve after adding the marks of the fourth subject is **60%**.