(1)4/15x75
=4x5
=20，(2)17/18X11/14 +19/18x11/14
=11/14x(17/18+19/18)
=11/14x36/18
=11/14x2
=11/7，(3)9/14x21x2/9
=9/2x3x2/9
=3，(4)8/9X3/5-1/4
=8/15-1/4
=32/60-15/60
=17/60，(5)3/5X5/9+3/8
=1/3+3/8
=8/24+9/24
=17/24，(6)4/5x5/8-4/5x5/12
=4/5x(5/8-5/12)
=4/5x(15/24-10/24)
=4/5x5/24
=1/6