Outputting Fractions
Frankly, it seems unnecessary to have any custom exceptions (and if you keep them, they should all have PEP-8-compliant names). All of the custom exceptions could just be ValueErrors ("when a built-in operation or function receives an argument that has the right type but an inappropriate value") with different messages, e.g.:

if not nums or not fractions: # note empty collections evaluate False in a boolean context
    raise ValueError("Null sample space")