if p ( a ) = 6 / 17 , p ( b ) = 5 / 17 , and p ( a ∪ b ) = 4 / 17 find p ( b | a ) ?
"p ( b | a ) = p ( a ∪ b ) / p ( a ) p ( b | a ) = ( 4 / 17 ) / ( 6 / 17 ) = 4 / 6 = 2 / 3 . a"
divide(divide(4, 17), divide(6, 17))