How can perform a summation?

[Leebo]

Is there a way to perform a summation expression in Excel?

For example, I need to sum 1 + 2 + 3 + 4 + 5. I can easily type 1
through 5 in five cells and use the SUM function but what if I need to
not sum 1 to 5, but rather 1 to n. Is there a summation function in
Excel that could perform this calculation?

 

[Guest]

The formula for that is n*(n+1)/2. So if the number you want to sum till is
in A1 and you want the reult in cell B1 then in cell B1 you will enter the
formula =A1*(A1+1)/2

Alok

 

[Guest]

That is assuming the numbers are in consecutive order. I know that's the way
the example stated but if your actual data isn't in consecutive order use the
following formula:

Assume your list of numbers is in A1:A1000 and your "n" value (how far down
you want to sum) is in B1. Enter this formula in any cell:

=SUM(OFFSET(A1,,,B1))

 

[RagDyer]

FWIW,

Might be of interest.

Originator of this arithmetic series formula (Gauss as a school boy):

http://mathworld.wolfram.com/ArithmeticSeries.html

Read the short paragraph at the end.<g>

 

[Leebo]

Thanks. Both responses are helpful. The link to the Gauss writeup wa
exactly what I was looking for.

::S::n=::1/2n(a1::+an)

So, if I have consequtive integers from A1 to An, I don't need to key
column of numbers to add up. Instead, just list the first and las
number, then use this formula.

If A1 = 1, B1 = 5

C1 = A2*(A1+A2)/2

then

C1 = 15

Thanks again for the help

 

[RagDyeR]

Appreciate the feed-back.
--

Regards,

RD
----------------------------------------------------------------------------
-------------------
Please keep all correspondence within the Group, so all may benefit !
----------------------------------------------------------------------------
-------------------

message
Thanks. Both responses are helpful. The link to the Gauss writeup was
exactly what I was looking for.

::S::n=::1/2n(a1::+an)

So, if I have consequtive integers from A1 to An, I don't need to key a
column of numbers to add up. Instead, just list the first and last
number, then use this formula.

If A1 = 1, B1 = 5

C1 = A2*(A1+A2)/2

then

C1 = 15

Thanks again for the help.