5/9*8+5/9*2
=5/9x(8+2)
=5/9x10
=50/9
(7/10+3/4)*5
=7/10x5+3/4x5
=7/2+15/4
=14/4+15/4
=19/4
135*8/9*3/4
=120x3/4
=90
6/11*7/8-6/8*6/11
=6/11x(7/8-6/8)
=6/11x1/8
=3/44
(21+2/5)*5/7
=21x5/7+2/5x5/7
=15+2/7
=15又2/7
2/5*51*1/10
=2/5x1/10x(50+1)
=1/25x50+1/25x1
=2+1/25
=2又1/25
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