计算下面各题,能简算的要用简便方法算.
0.75+1.25×2.4
5.67×0.21-0.62
3.8×6.7+3.3×3.8
1.28×0.29-0.29×0.28
101×4.8
4.89×99+4.89.解:(1)0.75+1.25×2.4
=0.75+(1.25×8)×0.3
=0.75+10×0.3
=0.75+3
=3.75;
(2)5.67×0.21-0.62
=1.1907-0.62
=0.5707;
(3)3.8×6.7+3.3×3.8
=3.8×(6.7+3.3)
=3.8×10
=38;
(4)1.28×0.29-0.29×0.28
=0.29×(1.28-0.28)
=0.29×1
=0.29;
(5)101×4.8
=(100+1)×4.8
=100×4.8+4.8
=480+4.8
=484.8;
(6)4.89×99+4.89
=4.89×(99+1)
=4.89×100
=489.
分析:(1)把2.4看作8×0.3,运用乘法分配律计算,然后再算加法;
(2)先算乘法,再算减法;
(3)(4)(6)运用乘法分配律简算;
(5)把101看作100+1,运用乘法分配律简算.
点评:此题考查了小数的四则混合运算,注意运算顺序和运算法则,灵活运用所学的运算律简便计算.
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