4. In a row of girls, Nivedita is 15th from the left and Vimla is 23rd from the right. If they interchange their positions, then Nivedita becomes 18 th from the left. Then at what position will Vimla be from the right?

The situation of positions can be depicted as follows:

 

... N (15L) . . . V (23 R) ...

 

Now, when they interchange their positions, then 

... V (?)    . . . N (18 L) ...

 

So, difference between their positions is 3 (18 - 15). That is, there are 3 people between both of them.

Thus, Vimla's position from right = 23 + 3 = 26th