Look at this series: 31, 29, 24, 22, 17, ... What number should come next?

Given data

• Series: 31, 29, 24, 22, 17, ...

Concept/ApproachAlternating differences: −2, −5, −2, −5, ...

Step-by-Step calculation31 − 2 = 2929 − 5 = 2424 − 2 = 2222 − 5 = 17Next: 17 − 2 = 15

Verification/AlternativeTwo-step cycle (−2, −5) repeats, so the next subtraction is −2.

Common pitfalls

• Subtracting another 5, which would break the pattern.

Final Answer15