Why Does This Mathematical Equality Hold True?

[cappadonza]

i'm going through a proof and i can't seem to workout why this equality makes sense
\sum^{10^{i}-1}_{k=0} \frac{k}{10^i} = \frac{(10^i-1)}{2}
this may be obvious, any hints atleast would be much appreciated

 

[NaturePaper]

This is just \sum\limits_{k=0}^{n-1}k=\frac{n(n-1)}{2}; in your problem, replace n \mbox{ by } 10^i.


By the way, your series is a finite one :)
Cheers.