"John Mansfield" wrote...
Excel provides no direct way to display the ratio between two values.
However, John Walkenbach's site shows how you can estimate a ratio via a
formula:

http://www.j-walk.com/ss/excel/usertips/tip81.htm
....

If the OP could live with '/' rather than ':', then standard fraction
numeric formatting would display ratios as fractions. As for the linked
article, it must be WAY OLD. The simplest approach is

=SUBSTITUTE(TEXT(x/y,"####/####"),"/",":")

Not as short as the GCD formula, but uses nothing but built-in functions, so
no ATP dependency. Also, Walkenbach is wrong about how this is stored. Both
formulas on his site and the formula above are all stored as text, not time
values. They may be converted into time values if used as arithmetic
operands, but it's simple enough to convert the ':' back to a '/' using

SUBSTITUTE(z,":","/")