7/8*5/6÷5/8
=7/8*5/6*8/5
=7/8*4/3
=7/6
24÷0.4÷2/3
=60÷2/3
=60*3/2
=902
2/15*3/4+2/3÷4/3
=2/15*3/4+2/3*3/4
=(2/15+2/3)*3/4
=4/5*3/4
=3/5
（2/17+1/3）÷5/51
=(2/17+1/3)*51/5
=2/17*51/5+1/3*51/5
=6/5+17/5
=23/5
4/9x=2/3
x=2/3÷4/9
x=2/3*9/4
x=3/2
1/2x+1/5x=14
(1/2+1/5)x=14
7/10x=14
x=14+7/10
x=14*10/7
x=20