Question

4．用簡便方法計(jì)算

3.4×9+3.4	1.25×0.5×8×0.2	7.5×101
0.25×3.68×40	4.2×3.7+6.3×4.2	5.5×9.8．

Answer 1

分析 ①⑤逆運(yùn)用乘法分配律可簡便計(jì)算，
②④運(yùn)用乘法交換律和結(jié)合律可簡便計(jì)算，
③⑥運(yùn)用乘法分配律可簡便計(jì)算，

解答 解：①3.4×9+3.4
=3.4×（9+1）
=3.4×10
=34

②1.25×0.5×8×0.2
=（1.25×8）×（0.5×0.2）
=10×0.1
=1

③7.5×101
=7.5×（100+1）
=7.5×100+7.5×1
=750+7.5
=757.5

④0.25×3.68×40
=0.25×40×3.68
=10×3.68
=36.8

⑤4.2×3.7+6.3×4.2
=4.2×（3.7+6.3）
=4.2×10
=42

⑥5.5×9.8
=5.5×（10-0.2）
=5.5×10-5.5×0.2
=55-1.1
=53.9

點(diǎn)評 此題考查小數(shù)四則混合運(yùn)算順序和靈活運(yùn)用運(yùn)算定律，分析數(shù)據(jù)找到正確的計(jì)算方法．