if p ( a ) = 2 / 15 , p ( b ) = 4 / 15 , and p ( a ∪ b ) = 6 / 15 find p ( a | b )
"p ( a | b ) = p ( a ∪ b ) / p ( b ) p ( a | b ) = ( 6 / 15 ) / ( 4 / 15 ) = 3 / 2 . c"
divide(divide(6, 15), divide(2, 15))