In a row of boys, if A is 10th from the left and B is 9th from the right, and A and B interchange their positions, A becomes 15th from the left. How many boys are there in the row? MCQ with Answer and Explanation

After interchange, A is at B's original position which is 15th from left. Originally B was 9th from right. So total = (position of A after swap from left) + (original position of B from right) - 1 = 15 + 9 - 1 = 23.