Try this formula:
=SUBSTITUTE(TEXT(A1/B1,"?/?"),"/",":")
Result:
A B C
33 11 3:1
25 5 5:1
6 4 3:2
Explanation:
The function TEXT(A1/B1,"?/?") converts A/B to an incorrect fraction.
SUBSTITUTE(...) substitutes a colon for the "/" in the fraction.
There are no special toolkits or macros required. The main drawback is that the result is text rather than a number, so you can easily utilise it in other calculations.