a)9/5 : (3/4•8/21+1)-4/9
=9/5:(2/7+7/7)-4/5
=9/5:9/7-4/9
=9/5•7/9-4/5=7/5-4/9=63/45-20/45
=43/45
b)(3/7:8/63-5/2)•8
=(3/7•63/8-5/2)•8
=(27/8-5/2)•8
=7/8•8/1=7
c)(1/12+1/24-1/36):(1/4+3/5)•17/7
=7/72:27/20•17/4
=7/72•20/27•17/4
=595/1944
d)(24/8+3/8):(4/35-1/20)•4/15
=27/8:9/140•4/15
=27/8•140/9•4/15
=3/2•140•1/15
=3/2•28•1/3
=1/2•28
=14
