27分之4*19分之5加27分之5*19分之15
=4/27X5/19+5/27X15/19
=5/27X4/19+5/27X15/19
=5/27X(4/19+15/19)
=5/27X19/19
=5/274/27X5/19为什么可以写成5/27X4/19乘法交换律4/27X5/19=(4X5)/(27X19)=(5X4)/(27X19)=5/27X4/19