Another excel question

[jimmy_onions]

For all you excel experts, another query which I would have thought would have been ridiculously straight forward, but excel seems to be coming up wanting....

Can you do a basic summation in excel, e.g. the sigma sign..sum of x from x=1 to x=n, where n varies...

e.g 1+2+3+4+.....n

would have thought this was trivial, but apparently not?

[Samdy Gray]

Where are you getting 'n' from? A cell value?

[jimmy_onions]

yes

[Samdy Gray]

And you want to add up all the numbers between 1 and n ?

[jimmy_onions]

yep

[Samdy Gray]

Use =sum((a1*(a1+1))/2), substitute a1 for the range of the cell where 'n' is stored.

[jimmy_onions]

samdy gauss, I mean gray...thanks a lot, that does the trick....what is your mathemtical background that you can pluck out equations like that at a drop of a hat?

That works perfectly for me, however I am still curious if there is a more general summation expression  in excel which will work for the summation of any function, not just x,   x^2, 3x/2,  x^3/x etc etc..

[Samdy Gray]

The basic equation for working out the sum of a 1 to n sequence is:

n(n+1)
   2

Basic GCSE maths.

You could probably use SERIESSUM (http://office.microsoft.com/en-gb/excel-help/seriessum-HP005209253.aspx) but that's more for when it's not exactly a simple series.

[jimmy_onions]

I did my gcse over 20 years ago...long since forgotten...cheers anyway.