(20-1/9)*(19-8/9)
=20*19-20*8/9-19*1/9+1/9*8/9
=380-160/9-19/9+8/81
=380-179/9+8/81
=380-19-8/9+8/81
=361-72/81+8/81
=361-64/81
=360又81分之17
(20-1/9)*(19-8/9)
=20*19-20*8/9-19*1/9+1/9*8/9
=380-160/9-19/9+8/81
=380-179/9+8/81
=380-19-8/9+8/81
=361-72/81+8/81
=361-64/81
=360又81分之17