Extend the alternating-difference series by two terms. Sequence: 36, 31, 29, 24, 22, 17, 15, ____ , ____
Verbal Reasoning
Number Series
Difficulty: Easy
Choose an option
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A13 11
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B10 5
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C13 8
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D12 7
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E10 8
Answer
Correct Answer: 10 8
Explanation
Introduction / Context:Many quantitative series alternate between two fixed negative differences. Identifying the cycle length and values lets you project future terms confidently.
Given Data / Assumptions:
- Series: 36, 31, 29, 24, 22, 17, 15
- Find the next two terms.
Concept / Approach:Calculate consecutive differences and look for an A-B-A-B pattern.
Step-by-Step Solution:
36→31: -531→29: -229→24: -524→22: -222→17: -517→15: -2Cycle is (-5, -2) repeating.Next after 15: -5 → 15 - 5 = 10.Then: -2 → 10 - 2 = 8.Verification / Alternative check:The derived pair 10, 8 maintains the exact alternating-difference rhythm.
Why Other Options Are Wrong:
- 13 11 / 12 7 / 13 8 / 10 5: Each mismatches the -5 then -2 cycle after 15.
Common Pitfalls:Assuming a constant difference or reversing the order of the alternating differences. Always write the last few steps explicitly.
Final Answer:10 8