Which number will replace the question mark (?) in the following series?
3, 4, 5, 6, 9, 10, 11, 12, 15, ?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 16
The differences between the terms follow a repeating pattern +1, +1, +1, +3: the series runs in blocks of four consecutive numbers, and each block starts 3 after the end of the last one.
3, 4, 5, 6: +1, +1, +1; then \(6+3=9\)
9, 10, 11, 12: +1, +1, +1; then \(12+3=15\)
15 starts a new block, so the next term is \(15+1=\) 16