In a row of students, Sunita is 9th from the left and Sohan is 12th from the right. When they interchange their places, Sunita became 19th from the left. How many students were there in a row?

Options

A. 27
B. 29
C. 30
D. 20

Explanation

To solve the problem, we need to determine the total number of students in the row based on the information given about Sunita and Sohan's positions.

1. **Identify Sunita's initial position**:
- Sunita is 9th from the left.

2. **Identify Sohan's position**:
- Sohan is 12th from the right.

3. **Determine Sunita's new position after the interchange**:
- After they interchange their places, Sunita becomes 19th from the left.

4. **Calculate Sohan's new position**:
- Since Sunita is now 19th from the left, we can find Sohan's position from the left when they switch places.
- Sohan's position from the left can be calculated as follows:
- Total number of students = Sunita's position from the left + Sohan's position from the right - 1
- Let’s denote the total number of students as \( N \).
- When Sunita was at 9th from the left, Sohan was at 12th from the right, so:
\[ N = 9 + 12 - 1 = 20 \]

5. **Verify with Sunita's new position**:
- Now, after the interchange, Sunita is 19th from the left, which means Sohan is now at the position:
\[ N - 19 + 1 = 20 - 19 + 1 = 2 \]
- This means Sohan is now 2nd from the left, which is consistent with the original information.

6. **Final Calculation**:
- Therefore, the total number of students in the row is \( N = 20 \).

### Final Answer:
There are **20 students** in the row.