In a row, A is in the $11\text{th}$ position from the left and B is in the $10\text{th}$ position from the right. If A and B interchange their positions, A becomes $18\text{th}$ from the left. How many persons are there in the row other than A and B?

Let's find the total number of individuals in the row step-by-step:
1. Initially, B's position is $10\text{th}$ from the right.
2. After interchanging, A moves to B's original position.
3. We are told that A's new position is $18\text{th}$ from the left.
4. Since this point corresponds exactly to B's original place, this specific location is $18\text{th}$ from the left and $10\text{th}$ from the right.

Using the total line positioning formula:

$$\text{Total number of persons}=\text{Position from Left}+\text{Position from Right}-1$$

$$\text{Total}=18+10-1=27$$

5. The question explicitly asks for the number of individuals other than A and B:

$$\text{Required answer}=\text{Total}-2=27-2=25$$