David, Hikmet, Jack, Marta, Rand, and Todd were in a -person race with other people. Rand finished places ahead of Hikmet. Marta finished place behind Jack. David finished places behind Hikmet. Jack finished places behind Todd. Todd finished place behind Rand. Marta finished in th place. Who finished in th place?
- A)
- B)
- C)
- D)
- E)
Answer
B
Key insight
Marta's 6th place anchors a chain: Jack 5th, Todd 3rd, Rand 2nd, then Hikmet is 6 behind Rand in 8th.
Solution
Only one clue gives an absolute position, so start there and follow the chain of relative clues. "Ahead" means a smaller place number, "behind" a larger one.
- Marta is th.
- Marta is behind Jack, so Jack is th.
- Jack is behind Todd, so Todd is rd.
- Todd is behind Rand, so Rand is nd.
- Rand is ahead of Hikmet, so Hikmet is th.
- David is behind Hikmet, so David is th.
The th-place finisher is Hikmet: .
Why this works
Relative clues form a chain; one absolute fact pins the whole chain down. Find the anchor, then translate each "ahead by " into subtract and each "behind by " into add . The six unnamed runners just fill the gaps and can be ignored.
The trap
Reversing 'ahead' and 'behind' (ahead means a smaller place number), which sends the chain the wrong way.
Common mistakes
- Reversing 'ahead' and 'behind' (ahead means a smaller place number), which sends the chain the wrong way.
- Stopping at David (th) or Rand and misreading which person the question asks about.
Techniques
Set up the equation/formula and compute; no special trick needed