NOTICE. While work is in progress, much
of this topic is incomplete. You can
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more information here. Thanks for your patience.Charley Kyd 
Math and trigonometry
SUMIF Function
Adds the cells in
a row or column, as specified by one criteria
by
Charley Kyd, MBA Microsoft Excel MVP, 20052014
The Father of Spreadsheet Dashboard Reports

SUMIF summarizes data in a range using one criteria.
Syntax
SUMIF(range, criteria,
sum_range)

range
Required. The range of cells for the criteria to evaluate.

criteria
Required. The criteria in the form of a number (like 50),
text (like "sales"), or expression as text (like ">=99").
Text must be enclosed in quotation marks (like: "sales").
You also can use the wildcard characters "?" (to match a
single character) and "*" (to match any number of
characters).

sum_range
Optional. The range of cells to add. If this argument is
omitted, SUMIF adds values in range.
Applies To
Excel 2003 and above
Remarks
Keep in mind that SUMIF, which allows one criteria, and
SUMIFS, which allows more than
one criteria, arrange their arguments in a different sequence.
For this reason, it's often more conventient to use the SUMIFS
function for even one criteria.
Examples
You can
download this example workbook here,
along with all other example workbooks I've completed for this
Excel help area.
Example 1:
SUMIF returns the sum of all values that are greater than 10.
Example 2:
Because no sum_range is specified, SUMIF must sum "Hats". But
"Hats" isn't numeric, so its sum is zero.
Example 3:
SUMIF returns the total for Hats in the Sum_Range.
Example 4:
The case of the Criteria doesn't matter. SUMIF still returns
the total for Hats in the Sum_Range.
Example 5:
SUMIF returns the sum of the Sum_Range values for Range
values that meet the Criteria, whether they're entered as
numbers or text.
Example 6:
SUMIF returns the sum of all numeric Codes greater than 75.
Here, the Range item "88" is ignored because it's entered as
text and has no numeric value.
Example 7:
SUMIF returns the sum for all Range items starting with "H"
and ending with "s".
Example 8:
SUMIF returns the sum of Sum_Range values for Range items
like t?es, where "?" can be any character.
Example 9:
SUMIF converts the date expressed as text in the Criteria
cell to a date serial number, then returns the proper value.
Example 10:
Here, the Criteria cell isn't empty. Instead, it contains a
singlequote ('). It also could contain a null string entered by
formula (=""). In either case, SUMIF returns the sum of the
Sum_Range values for Range cells that are empty.
Example 11:
SUMIF adjusts the Sum_Range to be in sync with the Range.
Here, when the Sum_Range is only one cell, SUMIF expands it
apply to the entire Range column.
Example 12:
SUMIF adjusts the Sum_Range to be in sync with the Range.
Here, when the Range is only one cell, SUMIF redues the
Sum_Range so that it corresponds with only that one Range cell.
Example 13:
SUMIF adjusts the Sum_Range to be in sync with the Range.
When the Range is one column, SUMIF contracts the Sum_Range to
be the same.
Other Help
