[4/7×(3/5-1/4)+3/10]÷0.5=[80/140×(84/140-35/140)+42/140]÷0.5=(80/140×49/140+42/140)÷0.5=(3920/19600+6020/19600)÷0.5=9940/19600÷0.5=0.507142857÷0.5=1.01428571循环小数－－－－－累死啦!...