Identify Incorrect Fibonacci Series Number

The Fibonacci series follows the rule where each number is the sum of the two preceding ones. We examine the provided series against this rule.

Given series: 1, 1, 2, 3, 6, 8, 13, 21,...

Let's apply the Fibonacci rule (sum of the previous two numbers):

• 1st term: 1
• 2nd term: 1
• 3rd term: $1 + 1 = 2$ (Matches)
• 4th term: $1 + 2 = 3$ (Matches)
• 5th term: $2 + 3 = 5$. The series shows 6. This is incorrect.
• 6th term: $3 + 5 = 8$. If the 5th term were correct (5), this would be 8. The series shows 8.
• 7th term: $5 + 8 = 13$. If the 5th term were correct (5), this would be 13. The series shows 13.
• 8th term: $8 + 13 = 21$. If the 5th term were correct (5), this would be 21. The series shows 21.

The number 6 disrupts the Fibonacci sequence. Replacing it with 5 ($2 + 3$) would correct the series.