In the following series, identify the number that needs to be changed to form the Fibonacci series:

1, 1, 2, 3, 6, 13, ...

Question

In the following series, identify the number that needs to be changed to form the Fibonacci series:

1, 1, 2, 3, 6, 13, 21

A. 5  B. 8  C. 6  D. 13

Accepted Answer

The number 6 (at position 5) needs to be changed to 5. Answer is C. 6. The Fibonacci sequence starting 1, 1, 2, 3, 5, 8, 13, 21 is well-known. Comparing term by term with 1, 1, 2, 3, 6, 13, 21, we see that position 5 has 6 instead of the correct Fibonacci value 5. So the number 6 needs to be replaced by 5. Once 6 is changed to 5, every subsequent term checks out: 3+5=8, 5+8=13, 8+13=21.