In a row of people standing in a waiting area, facing North, Hari stands seventh from the left end of the row and there are three people between him and the person standing at the exact centre of the row. How many people are standing in the row?

In a row of people standing in a waiting area, facing North,

Hari stands 7th from the left.

_ ,_,_,_, _ , _, Hari

There are 3 people between him and the person standing at the exact center of the row.

_ ,_,_,_, _ , _, Hari, _, _,_Middle person 

So, number each side of middle person will be same

So, Hari is 7th, the center person must be at position $$\rightarrow$$​7 + 4 = 11th from the left (because there are 3 people between them and one at the center).

Total number of people in the row:
If the center person is at the 11th position, then the total number of people in the row must be 2 × 11 – 1 = 21 (because the center person is at the middle position).
Thus, the total number of people standing in the row is 21.
The correct answer is (c). ​​