Ranking and order questions are pure formula questions: 3 to 4 in every OPSC ASO paper, each answerable in under 30 seconds. Learn these five formulas and the two traps.
Formulas
- Total = rank from top + rank from bottom − 1. Sam is 9th from the top and 38th from the bottom → 46 (ASO 2018).
- Same rank from both ends: total = 2 × rank − 1. 33rd from both ends → 65 (ASO 2025).
- Position from the other end = total − given position + 1.
- Persons between two people = difference of their positions (both counted from the same end) − 1. Convert one position first: R is 4th from the right in a row of 30, so 27th from the left; W is 10th from the left; between them are 27 − 10 − 1 = 16 (ASO 2021).
- Total when the number between them is given (no overlap) = left position + number between + right position. 14 + 4 + 7 = 25 (ASO 2015).
Interchange questions
After they swap places, A stands exactly where B stood. So A's new position and B's old position from the other end belong to the same place. A was 10th from the left and B 9th from the right; after the swap A is 15th from the left, so total = 15 + 9 − 1 = 23 (ASO 2018).
Shifting
Convert the position to the end you are asked about, then add or subtract the shift. 13th from the right in a row of 26 is 14th from the left; shifting 3 places to the left makes it 11th (ASO 2025).
Comparison puzzles (taller, heavier)
Write the people as a chain from highest to lowest and add each clue. Fixed clues first: "shorter than only G" means 2nd tallest.
Traps
- "Facing North" vs "facing South" swaps left and right only in seating questions, not in plain row counts.
- If an option says "cannot be determined", check whether the two people could overlap. If the data is complete, there is a definite answer.