8.4*28+8.4*72 1.25/5+0.25*20 4.75+8.4/2.4*20 7.6*0.25*4 【要求简便计算】

8.4*28+8.4*72=8.4*(28+72)=8.4*100=840
1.25/5+0.25*20=0.25+5=5.25
4.75+8.4/2.4*20=4.75+8.4/2.4*20=4.75+3.5*20=4.75+70=74.75
7.6*0.25*4=7.6*(0.25*4)=7.6*1=7.6
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8.4*28+8.4*72
=8.4×（28＋72）
=8.4×100
=840
1.25/5+0.25*20
=0.25＋5
=5.25
4.75+8.4/2.4*20
=4.75+21/6×20
=4.75+70
=74.75
7.6*0.25*4
=7.6×（0.25×4）
=7.6×1
=7.6