脱式计算(能简算的要简算).(1)12.5×(36-7.2)÷3.6                     (2)33.33×3334+22.22×9999(3)8.4×2012.1+(2012.1+12.5)×1.6(4)7.5×2.3+1.9×2.5+12.5×0.4(5)(1+1.2)+(2+1.2×2)+(3+1.2×3)+…+(99+1.2×99)+(100+1.2×100)

问题描述:

脱式计算(能简算的要简算).
(1)12.5×(36-7.2)÷3.6                     
(2)33.33×3334+22.22×9999
(3)8.4×2012.1+(2012.1+12.5)×1.6
(4)7.5×2.3+1.9×2.5+12.5×0.4
(5)(1+1.2)+(2+1.2×2)+(3+1.2×3)+…+(99+1.2×99)+(100+1.2×100)

(1)12.5×(36-7.2)÷3.6,
=12.5×36÷3.6-12.5×7.2÷3.6,
=12.5×10-12.5×2
=125-25,
=100;
                     
(2)33.33×3334+22.22×9999,
=33.33×3334+33.33×6666,
=33.33×(3334+6666),
=33.33×10000,
=333300;
(3)8.4×2012.1+(2012.1+12.5)×1.6,
=8.4×2012.1+2012.1×1.6+12.5×1.6,
=(8.4+1.6)×2012.1+12.5×0.8×2,
=10×2012.1+10×2,
=20121+20,
=20141;
(4)7.5×2.3+1.9×2.5+12.5×0.4,
=2.5×6.9+1.9×2.5+5,
=2.5×(6.9+1.9)+5,
=2.5×8.8+5,
=2.5×8×1.1+5,
=20×1.1+5,
=22+5,
=27;
(5)(1+1.2)+(2+1.2×2)+(3+1.2×3)+…+(99+1.2×99)+(100+1.2×100),
=1+2+3+…+99+100+1.2×1+1.2×2+1.2×3+…+1.2×99++1.2×100,
=(1+100)×100÷2+1.2×(1+100)×100÷2,
=5050+6060,
=11110.
答案解析:(1)先变形为12.5×36÷3.6-12.5×7.2÷3.6,再进行计算;
(2)先变形为33.33×3334+33.33×6666,再根据乘法分配律简便计算;
(3)先变形为8.4×2012.1+2012.1×1.6+12.5×1.6,再根据乘法分配律简便计算;
(4)先变形为2.5×6.9+1.9×2.5+5,再根据乘法分配律简便计算;
(5)先变形为1+2+3+…+99+100+1.2×1+1.2×2+1.2×3+…+1.2×99++1.2×100,再根据高斯求和公式和乘法分配律简便计算.
考试点:小数四则混合运算;运算定律与简便运算.
知识点: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.