39×9/14÷13/14÷18 =39×9/14×14/13×1/18(39和13约分,9和18约分,14和14约分） =3/2 =1.5 9/20×1/2+19/20÷2 =9/20×1/2+19/20×1/2 =(9/20+19/20)×1/2 =7/5×1/2 =7/10 （1/4+1/3÷1/2）÷1/5 =（1/4+2/3）÷1...