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.

Difficulty: Medium

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

Discussion & Comments

No comments yet. Be the first to comment!
Join Discussion