题目内容
计算,能简算的要简算
(1)13-1-1
(2)1-6÷3×
(3)75×80%+24×+0.8
(4)(++)×24
(5)42÷7
(6)1÷(+2+)
(7)33333×66666+77778×99999
(8)++++++.
解:(1)13-1-1,
=13-(1+1),
=13-3,
=10;
(2)1-6÷3×,
=1-6××,
=1-,
=;
(3)75×80%+24×+0.8,
=75×0.8+24×0.8+0.8,
=(75+24+1)×0.8,
=100×0.8,
=80;
(4)(++)×24,
=×24+×24+×24,
=8+4+15,
=27;
(5)42÷7,
=(42+)÷7,
=42÷7+÷7,
=6+×,
=6+,
=6;
(6)1÷(+2+),
=1÷,
=×,
=;
(7)33333×66666+77778×99999,
=33333×3×22222+77778×99999,
=99999×22222+77778×99999
=99999×(22222+77778),
=99999×100000,
=9999900000;
(8)++++++,
=-+-+-+-+-+-+-,
=1-,
=.
分析:(1)运用减法的性质简算;
(2)先算除法和乘法,再算减法;
(3)把百分数和分数化为小数,运用乘法分配律简算;
(5)把42拆成42+,运用除法的性质简算;
(6)先算括号内的,再算括号外的;
(7)把33333×66666=33333×3×22222=99999×22222,运用乘法分配律简算;
(8)通过观察,每个分数的分母为两个连续自然数的乘积,可以分别把它们拆分成两个分数相减的形式,然后通过加减相抵消的方法,求得结果.
点评:解答四则混合运算的题目,应仔细观察,根据题目的特点,灵活巧妙地解答.
=13-(1+1),
=13-3,
=10;
(2)1-6÷3×,
=1-6××,
=1-,
=;
(3)75×80%+24×+0.8,
=75×0.8+24×0.8+0.8,
=(75+24+1)×0.8,
=100×0.8,
=80;
(4)(++)×24,
=×24+×24+×24,
=8+4+15,
=27;
(5)42÷7,
=(42+)÷7,
=42÷7+÷7,
=6+×,
=6+,
=6;
(6)1÷(+2+),
=1÷,
=×,
=;
(7)33333×66666+77778×99999,
=33333×3×22222+77778×99999,
=99999×22222+77778×99999
=99999×(22222+77778),
=99999×100000,
=9999900000;
(8)++++++,
=-+-+-+-+-+-+-,
=1-,
=.
分析:(1)运用减法的性质简算;
(2)先算除法和乘法,再算减法;
(3)把百分数和分数化为小数,运用乘法分配律简算;
(5)把42拆成42+,运用除法的性质简算;
(6)先算括号内的,再算括号外的;
(7)把33333×66666=33333×3×22222=99999×22222,运用乘法分配律简算;
(8)通过观察,每个分数的分母为两个连续自然数的乘积,可以分别把它们拆分成两个分数相减的形式,然后通过加减相抵消的方法,求得结果.
点评:解答四则混合运算的题目,应仔细观察,根据题目的特点,灵活巧妙地解答.
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