I was recently doing a combinatorics problem, where we had to select 4 books from a set of 10 ,where the selected books are not adjacent to each other. The author put forward the idea of using a 10-digit binary number and the books to be selected were 1's and the others were 0's. While playing with the idea I eventually found that(Image above)

and so on, and thus followed the Fibonacci Sequence! Does anyone know why it is? Please share you opinions!

## Comments

Sort by:

TopNewestLet \(a_{n}\) be the number of n-digit binary numbers such that no 1's are together.

Now such number might end with 0 or 1

Case-1, It ends with 0 Now the number of such n-digit numbers will be \(a_{n-1}\)

Case-2, It ends with 1 Here, it cannot end with \(\boxed{11}\) block. It must be ending with \(\boxed{01}\) Number of such binary numbers will be \(a_{n-2}\)

Therefore \(a_{n}\)=\(a_{n-1}\) + \(a_{n-2}\) which is the condition for fibonacci series. – Pranjal Jain · 2 years, 1 month ago

Log in to reply