In a row of 39 people facing north, Lavanya sits 17th from the left end. If…

Concept — For a straight line of n people, the same person is counted from both ends, so the two counts always satisfy (position from the left) + (position from the right) = n + 1, i.e. position from the right = n − (position from the left) + 1. And "k places to the right of X" means k seats beyond X's own seat, so it adds k to X's count from the left.

Applying it here:

1. The row holds n = 39 people, and all of them face the same way (north), so a single left-to-right axis describes the whole row.

2. Lavanya's count from the left end is 17.

3. "5 places to the right of Lavanya" moves 5 seats past her own seat, so Rajat's count from the left end is 17 + 5 = 22.

4. Convert that into a count from the right end with the identity: 39 − 22 + 1 = 18.

5. So Rajat stands 18th from the right end of the row.

Cross-check:

• The two counts add up as the identity demands: 22 + 18 = 40 = 39 + 1.

• Counting people instead of using the formula: 39 − 22 = 17 people stand beyond Rajat towards the right end, so he is the 18th person when you start counting from that end.

Where the usual slips lead:

• 22 is Rajat's count from the LEFT end, which is the intermediate value, not the count from the right end that the question asks for.

• 21 comes from treating Lavanya's own seat as the first of the five steps (17 + 5 − 1 = 21), which again is a count from the left end.

• 19 is what that same inclusive slip gives after conversion: 39 − 21 + 1 = 19.

Hence Rajat's position, counted from the right end of the row, is 18th.