Difficulty: Easy
Correct Answer: 5
Explanation:
Introduction / Context:This is a classic ranks-and-positions puzzle. We know the total number of children and how Raju’s rank changes after moving three places to the right. We must recover his original (pre-shift) position from the left end.
Given Data / Assumptions:
Concept / Approach:Convert a right-end rank to a left-end rank using left_rank = N − right_rank + 1. Then undo the “shift right by 3” to retrieve the original left-end rank.
Step-by-Step Solution:
After shift, right-rank(Raju) = 8 ⇒ left-rank(after) = 15 − 8 + 1 = 8.A shift 3 to the right increases his left-rank by +3.So original left-rank(before) = 8 − 3 = 5.Verification / Alternative check:Place a simple index to confirm: if before he was at left position 5, moving three to the right lands him at position 8 from left; in a row of 15, that is indeed 8th from right (15 − 8 + 1 = 8).
Why Other Options Are Wrong:Values like 12 or 14 contradict the derived conversion; 6 would imply an after-shift left rank of 9, not matching the given 8th from right.
Common Pitfalls:Forgetting the +1 when converting between right-rank and left-rank; or subtracting rather than adding the shift when moving right.
Final Answer:5
Discussion & Comments