题目内容
写出计算的主要过程,能简便的要用简便方法计算.
12.75-+1
6.3÷[(4-0.07×50)×1]
45×(+-)
×0.8+÷1.25.
解:(1)12.75-+1,
=12.75-+1.25,
=12.75+1.25-,
=14-,
=13;
(2)6.3÷[(4-0.07×50)×1],
=6.3÷[(4-3.5)×1],
=6.3÷[(4-3)×1],
=6.3÷[(4-3)×1],
=6.3÷[1×1],
=6.3÷1,
=6.3×,
=4.9;
(3)45×(+-),
=45×+45×-45×,
=10+21-9,
=22;
(4)×0.8+÷1.25,
=×0.8+÷,
=×0.8+×0.8,
=(+)×0.8,
=1×0.8,
=0.8.
分析:(1)把1化为小数,运用加法交换律与结合律简算;
(2)按运算顺序先算小括号内的乘法,再算小括号内的减法,然后算中括号内的乘法,最后算中括号外的除法;
(3)运用乘法分配律简算;
(4)把1.25化为分数,然后把除法改为乘法,运用乘法分配律的逆运算简算.
点评:考查了运算定律与简便运算,四则混合运算.注意运算顺序和运算法则,灵活运用所学的运算律简便计算.
=12.75-+1.25,
=12.75+1.25-,
=14-,
=13;
(2)6.3÷[(4-0.07×50)×1],
=6.3÷[(4-3.5)×1],
=6.3÷[(4-3)×1],
=6.3÷[(4-3)×1],
=6.3÷[1×1],
=6.3÷1,
=6.3×,
=4.9;
(3)45×(+-),
=45×+45×-45×,
=10+21-9,
=22;
(4)×0.8+÷1.25,
=×0.8+÷,
=×0.8+×0.8,
=(+)×0.8,
=1×0.8,
=0.8.
分析:(1)把1化为小数,运用加法交换律与结合律简算;
(2)按运算顺序先算小括号内的乘法,再算小括号内的减法,然后算中括号内的乘法,最后算中括号外的除法;
(3)运用乘法分配律简算;
(4)把1.25化为分数,然后把除法改为乘法,运用乘法分配律的逆运算简算.
点评:考查了运算定律与简便运算,四则混合运算.注意运算顺序和运算法则,灵活运用所学的运算律简便计算.
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