用简便方法计算下面各题.①574-399 ②432-(154-68) ③672+516-72 ④78+76+83+82+77+80+79+85 ⑤
用简便方法计算下面各题.①574-399②432-(154-68)③672+516-72④78+76+83+82+77+80+79+85⑤321+(729-155)⑥72...
用简便方法计算下面各题.①574-399 ②432-(154-68) ③672+516-72 ④78+76+83+82+77+80+79+85 ⑤321+(729-155) ⑥725÷25.
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(1)574-399,
=574-400+1,
=175;
(2)432-(154-68),
=432+68-154,
=500-154,
=346;
(3)672+516-72,
=672-72+516,
=600+516,
=1116;
(4)78+76+83+82+77+80+79+85,
=80×8-2-4+3+2-3+0-1+5,
=640;
(5)321+(729-155),
=321+729-155,
=1050-155,
=895;
(6)725÷25,
=725÷5÷5,
=145÷5,
=29.
=574-400+1,
=175;
(2)432-(154-68),
=432+68-154,
=500-154,
=346;
(3)672+516-72,
=672-72+516,
=600+516,
=1116;
(4)78+76+83+82+77+80+79+85,
=80×8-2-4+3+2-3+0-1+5,
=640;
(5)321+(729-155),
=321+729-155,
=1050-155,
=895;
(6)725÷25,
=725÷5÷5,
=145÷5,
=29.
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