In a row of boys P is 28th from the left and Q is 17th from the right. They interchange their positions with each other and P become 42nd from the left. What is the position of Q from the right when he interchanged his position with P?

31

First of all, we have to find the total number of boys in the row,

Step 1:

T = L + R - 1

= 42 + 17 – 1

⇒ 58

Step 2: Now position of Q from the right is,

R = T – L + 1

= 58 – 28 + 1

⇒ 31