( 1 - 1/2 ) x ( 1 - 3/5 ) x ( 1 - 2/7 ) x ( 1 - 2/9 )
= 1/2 x 2/5 x 5/7 x 7/9
= 1 x 2 x 5 x 7/2 x 5 x 7 x 9
= 1/9.
\(=\dfrac{1}{2}\times\dfrac{2}{5}\times\dfrac{5}{7}\times\dfrac{7}{9}\)
\(=\dfrac{1}{5}\times\dfrac{35}{63}\)
\(=\dfrac{35}{315}\)
\(=\dfrac{1}{9}\)