Question

11．简算．

31.9÷0.2÷5	（0.25+2.5）×40	7.5×0.3+1.5×0.3+0.3
7.4×2.8-0.4×2.8	4.92÷（4.92×4）	39×10.1

Answer 1

分析 ①⑤根据除法的性质可简便计算；
②③④⑥运用乘法分配律可简便计算；

解答 解：①31.9÷0.2÷5
=31.9÷（0.2×5）
=31.9÷1
=31.9

②（0.25+2.5）×40
=0.25×40+2.5×40
=10+100
=110

③7.5×0.3+1.5×0.3+0.3
=0.3×（7.5+1.5+1）
=0.3×10
=3

④7.4×2.8-0.4×2.8
=2.8×（7.4-0.4）
=2.8×7
=19.6

⑤4.92÷（4.92×4）
=4.92÷4.92÷4
=1÷4
=0.25

⑥39×10.1
=39×（10+0.1）
=39×10+39×0.1
=390+3.9
=393.9

点评 此题考查小数的四则混合运算定律，分析数据找到合适的简便算法．