Look at this series: 3, 4, 7, 8, 11, 12, ... What number should come next?

Given data

• Series: 3, 4, 7, 8, 11, 12, ...

Concept/Approach
Alternating increments: +1, +3, +1, +3, +1, ...

Step-by-Step calculation
3 + 1 = 44 + 3 = 77 + 1 = 88 + 3 = 1111 + 1 = 12Next: 12 + 3 = 15

Verification/Alternative
View as two interleaved sequences of increments repeating every two steps.

Common pitfalls

• Assuming +2 repeating; that fails at 7 → 8.

Final Answer
15