Number series with a functional step: 48, 23, ?, 4.25, 1.125 Find the missing third term by identifying the rule applied at each step.

Difficulty: Easy

Correct Answer: 10.5

Explanation:


Introduction / Context:
Series sometimes evolve by repeatedly applying the same function rather than adding a constant difference. Here values drop sharply, hinting at a halving or fractional operation plus a small adjustment.



Given Data / Assumptions:

  • Known terms: 48, 23, ?, 4.25, 1.125
  • We search for a consistent term-to-term map f(x) that fits all given steps.


Concept / Approach:
Test simple transformations such as x/2, x/2 ± 1, or (x ± c)/k. Check whether one rule fits both 48 → 23 and 4.25 → 1.125. If so, apply it to 23 to recover the missing middle term.



Step-by-Step Solution:
Check 48 → 23 via x/2 − 1: 48/2 − 1 = 24 − 1 = 23 (fits).Check 4.25 → 1.125 via x/2 − 1: 4.25/2 − 1 = 2.125 − 1 = 1.125 (fits).Apply to 23 to get the missing term: 23/2 − 1 = 11.5 − 1 = 10.5.



Verification / Alternative check:
Forward: 10.5/2 − 1 = 5.25 − 1 = 4.25, consistent with the displayed continuation.



Why Other Options Are Wrong:
10, 2.5, and 11 do not satisfy the same function across all the checked steps; they would break the uniform mapping.



Common Pitfalls:
Assuming pure halving (x/2) without the small offset; testing only one transition and not validating against others.



Final Answer:
10.5

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