Question 1
In a row of 40 people, A is 13th from the left. After interchanging positions with B, A becomes 20th from the left. B originally was 15th from the right. What is A's new rank from the right?
After interchange, A's new left rank is 20. So A's new right rank = total - new_left + 1 = 40 - 20 + 1 = 21.