# Math Help - Converting a series to AP

1. ## Converting a series to AP

If i have a series of natural numbers then how many numbers must be added to this series so that the resulting series is in AP ?
E.g
1,3,7,13
then i need to add 3 numbers i.e 5,9 and 11 so the resulting series is in AP.

2. I think you would need to find the lowest arithmetic mean...

3. Originally Posted by Prove It
I think you would need to find the lowest arithmetic mean...
arithmetic mean would be simply sum of numbers / number of them so lowest of what?
could you please explain a bit ?

4. Originally Posted by pranay
If i have a series of natural numbers then how many numbers must be added to this series so that the resulting series is in AP ?
E.g
1,3,7,13
then i need to add 3 numbers i.e 5,9 and 11 so the resulting series is in AP.
Look for the greatest common divison of the first differences.

CB

5. Thank you all so much