0.9-(0.15+0.35÷7分之5)
=0.9-0.15-0.35*7/5
=0.75-0.7*0.7
=0.75-0.49
=0.26
(2-4分之3X5分之4)÷(12分之1+15分之4)
=(2-12/20)/(1/12+4/15)
=2/5/(5/60+16/60)
=2/5/(21/60)
=(2/5)*60/21
=8/7