Problem 11 · Parity · 3 points
Made by AI and not reviewed by a real person.
A toy crab starts on shell 5 in a row of shells numbered 1 to 11. It takes exactly four steps, each to a neighboring shell; which shell could it finish on?
- 7
- 6
- 8
- 11
- 4
Show a hint
- Each step switches between an odd and an even number.
Show the answer and solution
Answer: A — 7
The crab can reach 7 by stepping 5 → 6 → 7 → 8 → 7. After four steps from odd-numbered shell 5, it must finish on an odd number, so 4, 6, and 8 are impossible. Shell 11 is odd, but it is six steps away—too far for the crab to reach in four steps.