Number series – compute the next term using a “difference ×3 + 2” rule: 8, 10, 18, 44, 124, ? First differences follow d_{n} = d_{n-1} * 3 + 2.
Verbal Reasoning
Number Series
Difficulty: Medium
Choose an option
Answer
Correct Answer: 366
Explanation
Introduction / Context:Some non-linear series are governed by a recurrence on the differences, not the terms. Recognizing and extending that difference-recurrence gives the next value directly.
Given Data / Assumptions:
- Terms: 8, 10, 18, 44, 124, ?
- First differences: 2, 8, 26, 80, …
Concept / Approach:Model the first differences. Test d2=2*3+2=8; d3=8*3+2=26; d4=26*3+2=80. The fit is exact, so extend once more using the same rule.
Step-by-Step Solution:
Next difference: 80*3 + 2 = 242.Next term: 124 + 242 = 366.Verification / Alternative check:Back-substitute differences to reconstruct all terms; the recurrence holds at each step.
Why Other Options Are Wrong:
344/354/356 yield differences that are not 242, breaking d_{n}=3*d_{n-1}+2.Common Pitfalls:Trying multiplicative ratios on the terms; here the hidden structure is in the differences.
Final Answer:366