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?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 23
When A and B change places, A takes B’s old position. So A’s new place, 15th from the left, is the place where B stood, which is 9th from the right. With one place known from both ends, total \(=\) position from the left \(+\) position from the right \(-\,1\), because that person is counted twice.
Number of boys \(=15+9-1=23\)
A’s first position, 10th from the left, is not needed for the count.