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1.根据运算律填空。
(1)$4.2×1.69= □ ×□$
(2)$2.5×(0.77×0.4)= (□ ×□ )×□$
(3)$7.2×8.4+2.8×8.4= (□ +□ )×□$
(1)$4.2×1.69= □ ×□$
(2)$2.5×(0.77×0.4)= (□ ×□ )×□$
(3)$7.2×8.4+2.8×8.4= (□ +□ )×□$
答案
1.(1)1.69 4.2
(2)2.5 0.4 0.77
(3)7.2 2.8 8.4
(2)2.5 0.4 0.77
(3)7.2 2.8 8.4
2.用简便方法计算下面各题。
$78.5×12.5×0.8$ $4.6×7.8+2.2×4.6$ $0.25×4.53×4$
$78.5×12.5×0.8$ $4.6×7.8+2.2×4.6$ $0.25×4.53×4$
答案
2.=78.5×(12.5×0.8)=78.5×10=785
=4.6×(7.8+2.2)=4.6×10=46
=(0.25×4)×4.53=4.53
=4.6×(7.8+2.2)=4.6×10=46
=(0.25×4)×4.53=4.53
3.下面这道题计算得对吗? 正确画“√”,错误画“×”,并写出正确的计算过程和结果。
$50.4×1.9-1.8$
$=50.4×0.1$
$=5.04$()
$50.4×1.9-1.8$
$=50.4×0.1$
$=5.04$()
答案
3.× 50.4×1.9−1.8=95.76−1.8=93.96
