3÷3/4-3/4÷3=4-1/4=15/4
（3/4-5/8）÷5/9=1/8÷5/9=5/72
2/3-1/2÷5/3*5/6=2/3-25/36=-1/36
(2/3-1/2)÷5/3*5/6=1/12
(2/3-1/2)÷(5/3*5/6)=1/6÷25/18=3/25
(2/3-1/2÷5/3)*5/6=11/30*5/6=11/36
387*5/9+387*4÷9=387*(4/9+5/9)=387
(1/69+1/92)*23+5/12=1/69*23+1/92*23+5/12=1/3+1/4+5/12=1