Question: I want to sum cells that have a "C" and a decimal number. The cells
have other numbers and variables in them as well, but I only want to add ones
with "C"s.

Example of what cells contain:
7.5 C
H
7.5
9.4 C
3.2 F
HV
V
4.7 C

Answer:

Sum-text-cells-using-criteria-in-excel

Formula in B10:

=SUM(IF(ISNUMBER(SEARCH("C", A1:A8)), (LEFT(A1:A8, SEARCH("C", A1:A8)-2)*1), 0)) + CTRL + SHIFT + ENTER

Download excel sample file for this tutorial.
Sum text cells using criteria.xls
(Excel 97-2003 Workbook *.xls)

Functions in this article:

ISNUMBER(value)
Checks whether a value is a number and returns TRUE or FALSE

SUM(number1,[number2],)
Adds all the numbers in a range of cells

SEARCH() Returns the number of the character at which a specific character or text string is first found, reading left to right (not case sensitive)

IF(logical_test;[value_if:true];[value_if_false])
Checks whether a condition is met, and returns one value if TRUE, and another value if FALSE

LEFT(text;num_chars) Returns the specified number of characters from the start of textstring