Looking at the series: 3, 4, 5, 6, 9, 10, 11, 12, 15, ?
The series can be broken into groups of consecutive numbers:
Group 1: 3, 4, 5, 6
Group 2: 9, 10, 11, 12
Group 3: 15, ?, ?, ?
Each group contains 4 consecutive integers.
The starting number of each group follows a pattern:
- First group starts at 3
- Second group starts at 9 (difference of 6)
- Third group starts at 15 (difference of 6)
Following the pattern, the third group should be: 15, 16, 17, 18
Therefore, the number that replaces the question mark is 16.
The answer is Option 1: 16