题目内容
脱式计算,能简算的要简算: ×+÷ | [-(-)]× |
9999+9998+9997+9996 | 812-700÷(9+31×11) |
1.25×3.6×8×2.5-12.5×2.4 | +7.4-+3.6. |
解:(1)×+÷,
=×+×,
=×(+),
=×1,
=;
(2)[-(-)]×,
=[-]×,
=×,
=;
(3)9999+9998+9997+9996,
=(10000-1)+(10000-2)+(10000-3)+(10000-4),
=40000-10,
=39990;
(4)812-700÷(9+31×11),
=812-700÷(9+341),
=812-700÷350,
=812-2,
=810;
(5)1.25×3.6×8×2.5-12.5×2.4,
=1.25×3.6×8×2.5-1.25×24,
=1.25×(3.6×8×2.5-24),
=1.25×[3.6×2×(4×2.5)-24],
=1.25×[7.2×10-24],
=1.25×48,
=1.25×8×6,
=10×6,
=60;
(6)+7.4-+3.6,
=(-)+(7.4+3.6),
=+11,
=11.
分析:(1)把除法改为乘法,运用乘法分配律简算;
(2)先算小括号内的,再算中括号内的,最后算括号外的;
(3)把原式变为(10000-1)+(10000-2)+(10000-3)+(10000-4),运用加法结合律简算;
(4)先算括号内的乘法,再算括号内的加法,然后算括号外的除法,最后算减法;
(5)把原式变为1.25×3.6×8×2.5-1.25×24,运用乘法分配律简算;
(6)运用加法交换律与结合律简算.
点评:此题考查了四则混合运算,注意运算顺序和运算法则,灵活运用所学的运算定律进行简便计算.
=×+×,
=×(+),
=×1,
=;
(2)[-(-)]×,
=[-]×,
=×,
=;
(3)9999+9998+9997+9996,
=(10000-1)+(10000-2)+(10000-3)+(10000-4),
=40000-10,
=39990;
(4)812-700÷(9+31×11),
=812-700÷(9+341),
=812-700÷350,
=812-2,
=810;
(5)1.25×3.6×8×2.5-12.5×2.4,
=1.25×3.6×8×2.5-1.25×24,
=1.25×(3.6×8×2.5-24),
=1.25×[3.6×2×(4×2.5)-24],
=1.25×[7.2×10-24],
=1.25×48,
=1.25×8×6,
=10×6,
=60;
(6)+7.4-+3.6,
=(-)+(7.4+3.6),
=+11,
=11.
分析:(1)把除法改为乘法,运用乘法分配律简算;
(2)先算小括号内的,再算中括号内的,最后算括号外的;
(3)把原式变为(10000-1)+(10000-2)+(10000-3)+(10000-4),运用加法结合律简算;
(4)先算括号内的乘法,再算括号内的加法,然后算括号外的除法,最后算减法;
(5)把原式变为1.25×3.6×8×2.5-1.25×24,运用乘法分配律简算;
(6)运用加法交换律与结合律简算.
点评:此题考查了四则混合运算,注意运算顺序和运算法则,灵活运用所学的运算定律进行简便计算.
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