SUM(...)/A1
How to sum number from either of the two cells.
Used Functions
Category: Math and trigonometry
Adds its arguments
Syntax
SUM(number1,[number2],...)
Practice SUM Formula at Sheetzoom
SUM formula at Microsoft helpCategory: Logical
Specifies a logical test to perform
Syntax
IF(Something is True, then do something, otherwise do something else)
Category: Information
Returns TRUE if the value is a number
Syntax
ISNUMBER(value)
0
The formula checks if either of the cell has a numeric value, if it has, the value is returned, otherwise "...". The SUM() formula sums the value that is divided by value in cell A1.