Question

6．用遞等式計(jì)算．（能簡算的要簡算）
20.9+10.5÷（5.2-3.5）
3.5×0.7+5.5×0.7+0.7
10.64+7.65×2.4+11.76
6.2×9.9
0.125×3.2×0.25
9.83×（3.8-2.3）+1.5×6.17
21÷0.25÷0.4．

Answer 1

分析 ①先算小括號里面的算式，再算除法最后算加法．
②用乘法分配律計(jì)算即可．
③先算除法算式，再從左往右計(jì)算即可．
④把9.9變成10-0.1，再運(yùn)用乘法結(jié)合律計(jì)算，即6.2×9.9=6.2×（10-0.1）=6.2×10-0.1×6.2．
⑤把3.2看作8×0.4，再運(yùn)用乘法結(jié)合律計(jì)算，即（0.125×8）×（0.25×0.4）．
⑥先算小括號里面的算式，再用乘法分配律計(jì)算即可．
⑦用連除的性質(zhì)計(jì)算即可．a(chǎn)÷b÷c=a÷（b×c）．

解答 解：①20.9+10.5÷（5.2-3.5）
=20.9+10.5÷1.7
=20.9+6$\frac{3}{17}$
=27$\frac{13}{170}$

②3.5×0.7+5.5×0.7+0.7
=（3.5+5.5+1）×0.7
=10×0.7
=7

③10.64+7.65×2.4+11.76
=10.64+18.36+11.76
=29+11.76
=40.76

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

⑤0.125×3.2×0.25
=0.125×8×0.4×0.25
=（0.125×8）×（0.4×0.25）
=1×0.1
=0.1

⑥9.83×（3.8-2.3）+1.5×6.17
=9.83×1.5+1.5×6.17
=（9.83+6.17）×1.5
=16×1.5
=4×（4×1.5）
=4×6
=24

⑦21÷0.25÷0.4
=21÷（0.25×0.4）
=21÷0.1
=210

點(diǎn)評 此題考查了學(xué)生對小數(shù)四則混合運(yùn)算題的計(jì)算能力，以及靈活巧算的能力．