Just using my imagination here.
Are asking how to represent a vaule as "1/n"?
If you have a value in A1
="1/"&1/A1
If A1=4, this returns 1/0.25
or if if A1=0.25, this is 1/4
If this is what you're looking for you might to use a round on A1
="1/"&1/round(A1,<#ofdigits>)
I'd be curious to hear if there is a way customer format this.
