递等式计算(能简便的要简便)???
①25.3×12-33.46÷0.35??????
②12.74-0.125+2.26-9.875??????
③(+)÷
④2.5×13×0.4
⑤÷[(+)×]
⑥+×19.
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解:①25.3×12-33.46÷0.35?
=303.6-95.6
=208;
②12.74-0.125+2.26-9.875????
=(12.74+2.26)-(0.125+9.875)
=15-10
=10;
③(+)÷
=(+)×24
=×24+×24
=9+20
=29;
④2.5×13×0.4?
=2.5×0.4×13
=1×13
=13;
⑤÷[(+)×]
=÷(×)
=÷
=
=;
⑥+×19
=(1+19)×
=20×
=16.
解析分析:①按照先算乘除再算加减的法则运算;
②运用加法结合律计算;
③先变成乘法,再运用乘法分配律简算;
④运用乘法交换律简算;
⑤先算小括号,再算中括号的法则运算;
⑥运用乘法分配律简算.
点评:熟记各种运算定律,特别是乘法分配律和结合律.这是常用的简算方法.