(7/15-1/3)÷(1/3+1/5) =(7-5)÷(5+3)=1/4 (3/4+1/2)÷5/8 =3/4x8/5+1/2x8/5=6/5+4/5=2 2/13+3/4÷9/10+1/6=2/13+5/6+1/6=2/13+1=1又2/13 [3/4-(5/8-1/4)]÷3/8=(3/4+1/4-5/8)x8/3=3/8x8/3=1