In a certain code, 5 is written as 25 and 6 is written as 36. What is 9 written as?

  • A. 18
  • B. 81
  • C. 90
  • D. 99

Explanation

Each number is squared, since 5 squared is 25 and 6 squared is 36, so 9 becomes 81. Doubling would give 18, which is the trap in the first option. Always test a rule against every example given rather than only the first.

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