脱式计算,能简算的要简算.
(1)25×3.2×125
(2)
(3)÷
(4)×20+8÷
(5)5×(-)÷
(6)42÷(+)
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解:(1)25×3.2×125
=25×(4×0.8)×125,
=(25×4)×(0.8×125),
=100×100,
=10000;
(2)×99+
=×99×1,
=×(99+1),
=×100,
=4;
(3)÷
=×,
=×(+),
=×1,
=;
(4)×20+8÷
=×20+8×,
=×(20+8),
=×28,
=16;
(5)5×(-)÷
=5×(-)×,
=(-)×12,
=×12-×12,
=4-2.4,
=1.6;
(6)42÷(+)
=42÷(+),
=42÷,
=42×,
=36.
解析分析:(1)可将3.2改写成4×0.8的形式,然后再根据乘法结合律计算;
(2)、(3)、(4)、(5)可利用乘法分配律进行计算;
(6)根据四则混合运算的顺序进行计算.
点评:此题主要考查的是乘法分配律和乘法结合律在算式运算中的应用.