计算下列各题,能简算要简算(脱式计算）

7/8-5/6*9/10
=7/8-3/4
=7/8-6/8
=1/8
3/4÷（1-1/2-3/8)
=(3/4×8)÷[(1-1/2-3/8)×8]
=6÷(8-4-3)
=6÷1
=6
2-8/9*2/7*3/8
=2-2/21
=40/21
7/15÷[1-(4/5-2/3)]
=7/15÷(1-4/5+2/3)
=(7/15×15)÷[(1-4/5+2/3)×15]
=7÷(15-12+10)
=7÷13
=7/13
1/4+(5/8-3/10)*1/13
=1/4+(25/40-12/40)*1/13
=1/4+13/40*1/13
=1/4+1/40
=10/40+1/40
=11/40