You make it way too hard, just memorise this stuff:

Flop
FD - 35%
SD - 31%
SFD - 54%

Turn
FD - 20%
SD - 17%
SFD - 32%

Or round it off even more.

Flop
SD or FD - 1/3 chance of hitting.
SFD - Favorite to win hand.

Turn
SD or FD - 1/5 chance of hitting
SFD - 1/3 chance of hitting.


Like I say, approximate is fine unless you're playing hands with cards face up.