Question

5．計算下面各題，能簡便得要用簡便方法計算

21.36÷0.8-12.9	（4.2+3.5）÷0.7	0.74×0.99
5.5×17.3+6.7×5.5	0.32×25×12.5	4.9÷0.25÷0.4．

Answer 1

分析 ①先算除法再算減法．
②先算加法再算除法．
③把0.99變成1-0.01，再用乘法分配律計算．
④用乘法分配律計算．a(chǎn)×c+b×c=（a+b）×c．
⑤把0.32變成0.08×4，先算25×4得100，再算0.08×12.5得1，再用100×1即可．
⑥用連除的性質(zhì)計算，a÷b÷c=a÷（b×c）．

解答 解：①21.36÷0.8-12.9
=26.7-12.9
=13.8
②（4.2+3.5）÷0.7
=7.7÷0.7
=11
③0.74×0.99
=0.74×（1-0.01）
=0.74×1-0.74×0.01
=0.74-0.0074
=0.7326
④5.5×17.3+6.7×5.5
=5.5×（17.3+6.7）
=5.5×24
=132
⑤0.32×25×12.5
=0.08×4×25×12.5
=（4×25）×（0.08×12.5）
=100×1
=100
⑥4.9÷0.25÷0.4
=4.9÷（0.25×0.4）
=4.9÷0.1
=49

點評 本題利用具體的算式考查了學生對于簡便運算的掌握情況．