(3.6*2.1+3.5*2.4)/(10.5*7.2)
=(3.6*2.1+0.5*7*0.3*8)/(10.5*7.2)
=(3.6*2.1+4*2.1)/(10.5*7.2)
=(7.6*2.1)/(10.5*7.2)
=7.6/(5*7.2)
=7.6/36
=76/360
=19/90有简便方法吗已经够简便了!好吧.....