SOLUTION: What is the sum of all natural counting numbers from 1-9 inclusive

Question 785568: What is the sum of all natural counting numbers from 1-9 inclusive

Answer by KMST(5328) (Show Source): You can put this solution on YOUR website!
I would add those 9 numbers twice and then divide by 2.

Rearranging them in pairs, matching them head to tail, I get nine sums added up
=
and each of them adds to 10
=

Your teacher will say that the sequence of numbers from 1 to 9 is an arithmetic sequence (or an arityhmetic progression, depending on where you go to school), and to apply formulas like
,

and

and that for the numbers from 1 to 9,
, ,
If I had to deal with that, I would use

and calculate

which is exactly what I did above (but without the formulas).
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