2.4*1.25*0.3和842.4*6.7+8.24*31+0.824*20的简便运算怎么算

2.4*1.25*0.3
=0.8*1.25*0.3*0.3
=0.09
842.4*6.7+8.24*31+0.824*20
=84.24*67+8.24*31+8.24*2
=(76+8.24)*67+8.24*33
=76*67+8.24*67+8.24*33
=5092+8.24*100
=5092+824
=5916

2.4*1.25*0.3
=3×0.8×1.25×0.3
=3×0.3×1
=0.9
842.4*6.7+8.24*31+0.824*20
=8.24×（67+31+2）
=8.24×100
=824