What is an example of a modified Fibonacci sequence?

Question

Options

• A...5,8, 13,21,34...
• B... 2,4,5,9, 11...
• C-.5,8, 13, 20,40...
• D-I, 1,3,5,5...

• B
  3% (1)
• C
  95% (36)
• D
  3% (1)

Explanation

Option C (5, 8, 13, 20, 40) qualifies as a modified Fibonacci sequence because it begins with the correct Fibonacci addition rule - 5 + 8 = 13 - but then intentionally deviates from it (8 + 13 should be 21, not 20), signaling that the generating rule has been altered. Option A is a trap: it shows a perfectly standard Fibonacci sequence (5+8=13, 8+13=21, 13+21=34) with zero modification, making it the most tempting wrong answer. Options B (2, 4, 5, 9, 11) and D (−1, 1, 3, 5, 5) are disqualified because they never consistently establish the Fibonacci addition rule in the first place - B breaks immediately (2+4=6≠5) and D does the same (−1+1=0≠3), so neither can be a modification of something they never followed. Memory tip: A modified Fibonacci sequence must first prove it knows the rule (at least one correct sum) before breaking it - if it never follows the pattern at all, it's just a random sequence, not a modification.

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