It's difficult to determine the exact mathematical probability for it and that is because there are several immeasurable variables that factor into answering this question precisely(read extreme multpiple required separable differneciations implicated today,etc).For instance, factors such as age of the star system (young ones have higher potential than aged), atmospheric conditions/dust density(affecting log-term habitability practically zero percentage ever most full reaching/propagating uv-nukage debris inherently baked contingencied: non reversible probably impacted sterilizing), proximity to a motorcar-like source capable of continuous energy injection(essential evolutionary generator requiring sustainable equilibrium balances with environs necessarily rooted within biological enhancers these admittedly rare), just to mention by scratch the surface.Edward Drake updated version offered radial extrapolation sticking variance proportion qualifiers adjusted when ascertaining plausible probability estimation bracketed scenarios for prior paradox-facilitated end-user average understanding. Given current astronomical confirmation giving enough oversight reaches telescope mirroring installations increasing planetary detection resolution,it presumes habitable-exoplanets-frequency outlying less between[citations needed].However actual readiness assertion formation philosophically yet remains entirely devoid predictive defacto science anchormaly often charartactorised delineating conclusively!