Question

20．能簡(jiǎn)便計(jì)算要簡(jiǎn)便算
12.6×8.4-2.6×8.4      
0.4×1.7×2.5          
4.8×2.5
6.2×9.9         
9.83×1.5+15×0.017      
4.35+6.5÷0.13．

Answer 1

分析 ①⑤逆用乘法分配律簡(jiǎn)算，
②運(yùn)用乘法交換律和結(jié)合律簡(jiǎn)算，
③④運(yùn)用乘法分配律簡(jiǎn)算，
⑥先算除法，再算加法．

解答 解：①12.6×8.4-2.6×8.4 
=8.4×（12.6-2.6）
=8.4×10
=84     

②0.4×1.7×2.5 
=（0.4×2.5）×1.7
=1×1.7
=1.7         

③4.8×2.5
=（4+0.8）×2.5
=4×2.5+0.8×2.5
=10+2
=12

④6.2×9.9 
=6.2×（10-0.1）
=6.2×10-6.2×0.1
=62-0.62
=61.38        

⑤9.83×1.5+15×0.017 
=9.83×1.5+1.5×0.17
=（9.83+0.17）×1.5
=10×1.5
=15 
    
⑥4.35+6.5÷0.13
=4.35+50
=54.35

點(diǎn)評(píng) 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．