6.5*2.1-0.65 和 3.12+31.2*9.9 有简便算法么,怎么算.
问题描述：
6.5*2.1-0.65 和 3.12+31.2*9.9 有简便算法么,怎么算.
答
6.5(2.1-0.1)=13
31.2(0.1+9.9)=312
答
有的
6.5*2.1-0.65 =0.65 *21-0.65=0.65*20=13
3.12+31.2*9.9=3.12+3.12*99=3.12*100=312
答
6.5*2.1-0.65
=6.5*2.1-6.5*0.1
=6.5*（2.1-0.1)
=6.5*2
=13
3.12+31.2*9.9
=3.12+3.12*99
=312*(1+99)
=3.12*100
=312
答
6.5*2.1-0.65
=6.5*(2.1-0.1)
=6.5*2
=13
3.12+31.2*9.9
=3.14*(1+99)
=3.14*100
=312