题目内容

20.能用简便方法计算的用简便方法计算.
18.5-3.21-4.79                   4.8+3.72+4.2+16.28
4.5×0.7+5.5×0.7                      (8-0.8)×1.25
14.2×99+1.42                     8.8×0.6+0.32

分析 (1)利用减法性质计算;
(2)利用加法交换律与结合律计算;
(3)、(4)、(5)利用乘法分配律计算;
(6)先算乘法,后算加法.

解答 解:(1)18.5-3.21-4.79 
=18.5-(3.21+4.79)
=18.5-8
=10.5

(2)4.8+3.72+4.2+16.28
=(4.8+4.2)+(3.72+16.28)
=9+20
=29

(3)4.5×0.7+5.5×0.7 
=0.7×(4.5+5.5)
=0.7×10
=7

(4)(8-0.8)×1.25
=8×1.25-0.8×1.25
=10-1
=9

(5)14.2×99+1.42 
=14.2×99+14.2×0.1
=14.2×(99+0.1)
=14.2×99.1
=1407.22

(6)8.8×0.6+0.32
=5.28+0.32
=5.6

点评 考查学生对四则运算法则以及运算定律的掌握情况.

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