Re: Finding sum of all digits from 1 to 1 million.

use the formul ...
<RB> (n+1)*n/2

Why does this work?
look at this ... 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 is the same as

1 + 10 +
2 + 9 +
3 + 8 +
4 + 7 +
5 + 6
which is the same as
11 + 11 + 11 + 11 + 11
which is 11*5 = (n+1)*n/2 where n = 10

Comment on Re: Finding sum of all digits from 1 to 1 million.

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Re: Re: Finding sum of all digits from 1 to 1 million. by little (Curate) on Jan 24, 2002 at 16:40 UTC
Sorry, but 10 is not a gidit , its a number, composed of the digits 1 and 0. so your solution should look alike: 0+9 1+8 2+7 3+6 4+5 which is 45 But anyway, I wouldn't be surprised if another one shows up presenting a "correct" solution of "42" grin Have a nice day All decision is left to your taste	[reply]