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9. What two numbers should replace the question marks?
  24 29 26 31 28 ? ?
 

Explanation:
Sequence: + 5, - 3, + 5, - 3, ... (24 + 5 = 29; 29 - 3 = 26; ...; 28 + 5 = 33; 33 - 3 = 30).