Select the number that can replace the question mark [?] in the following series.
Show answer & explanation
Correct answer: C
Explanation
Pattern: Third number = First number + 3 × Second number
15 + 3×8 = 39
20 + 3×9 = 47
25 + 3×10 = 55
Therefore, the missing number is 55.
The correct answer is option (3).