In a row of boys, if A who is tenth from the left and B who is ninth from the right, interchange their positions, A becomes fifteenth from the left. How many boys are there in the row?

23

The correct answer is Option (1) → 23

Step 1: Let total number of boys = n

• A = 10th from left
• B = 9th from right

After interchanging, A becomes 15th from left.

Step 2: Find B’s original position in terms of A

• Distance moved by A to right = 15 - 10 = 5 positions
• So B’s original position from left = 15th from left (because A and B swapped)
• But B’s original position from left = n - 9 + 1 = n - 8

$n−8=15⟹n=23$