Ravi obtained 70 and 75 marks in first two unit test. Find the minimum marks he should get in the third test to have an average of at least 60 marks.

Explanation

To find the minimum marks Ravi should get in the third test to have an average of at least 60 marks, we can follow these steps:

1. **Understand the average formula**: The average of three tests can be calculated using the formula:
\[ \text{Average} = \frac{\text{Sum of marks}}{\text{Number of tests}} \]

2. **Set up the equation**: Ravi's marks in the first two tests are 70 and 75. Let \( x \) be the marks he needs in the third test. The average should be at least 60. Therefore, we can set up the inequality:
\[ \frac{70 + 75 + x}{3} \geq 60 \]

3. **Multiply both sides by 3**: To eliminate the fraction, multiply both sides of the inequality by 3:
\[ 70 + 75 + x \geq 180 \]

4. **Combine the known marks**: Add the marks from the first two tests:
\[ 145 + x \geq 180 \]

5. **Isolate \( x \)**: Subtract 145 from both sides to solve for \( x \):
\[ x \geq 180 - 145 \]
\[ x \geq 35 \]

6. **Conclusion**: Therefore, Ravi needs to score at least 35 marks in the third test to achieve an average of at least 60 marks.

### Summary of Steps:
1. Understand the average formula.
2. Set up the inequality based on the average requirement.
3. Multiply to eliminate the fraction.
4. Combine the known marks.
5. Isolate \( x \) to find the minimum required marks.
6. State the conclusion.