Puzzle-8 (SNAP-2008)

In a row at a bus stop, A is 7th from the left and B is 9th from the right. They both interchange their positions. A becomes 11th from the left. How many people are there in the row?
(A)  18        (B)  19           (C)  20        (D) 21
Solution follows here:

Solution:

Initial positions:

A is 7^th from left and B is 9^th from right and it is not clear about number of people between A and B

_  _  _  _  _  _  A ? B  _  _  _  _  _  _  _  _

Positions after interchange of A and B:

A is 7^th from left

      _  _  _  _  _  _  B  _  _  _  A  _  _  _  _  _  _  _  _

After interchange of A and B positions, it is very clear that there are 19 people in total.

"The Smarter Approach"

A's new position = B's old position

Let us concentrate on this position only. 

"9th from right and 11th from left" 

this means ---> 8 persons to the right and 10 persons to the left of that position.

Including that position, the total count  = 8+10+1 = 19 

Answer (B)