Copyright © University of Cambridge. All rights reserved.

'Fibonacci Deduction' printed from https://nrich.maths.org/

Show menu


_ , _ , _ , 6 , _ , 15

Let the fifth number be $x$:

_ , _ , _ , 6 , $x$ , 15

The sixth number is $6+x= 15$, so $x=9$.

_ , _ , _ , 6 , 9 , 15
 
The seventh number is the sum of the fifth and sixth numbers, $9+15=24$:

_ , _ , _ , 6 , 9 , 15 , 24
 
 
This problem is taken from the UKMT Mathematical Challenges.
You can find more short problems, arranged by curriculum topic, in our short problems collection.