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In the series 7, 9, 13, 21, 36, 69, 133, one number is wrong. Which is the wrong number?

Competition practiceNumber Series
  • A69
  • B133
  • C36
  • D21

Step-by-Step Solution

Differences should double: +2, +4, +8, +16, +32, +64. So after 21 the term should be 21 + 16 = 37, not 36. The wrong number is 36.
Answer: C) 36

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