Question

【題目】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

【答案】

①20.9+10.5÷（5.2﹣3.5）

=20.9+10.5÷1.7

=20.9+6

=27

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

【解析】

試題分析：①先算小括號(hào)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(hào)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：①20.9+10.5÷（5.2﹣3.5）

=20.9+10.5÷1.7

=20.9+6

=27

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