解题思路:(1)(2)(3)(4)(9)根据乘法分配律计算;
(5)根据乘法交换律和结合律计算;
(6)根据乘法结合律计算;
(7)变形为(0.125×8)×(4×2.5)计算;
(8)先变形为8×6.3-8×5.3,再根据乘法分配律计算.
(1)28.4×99+28.4
=28.4×(99+1)
=28.4×100
=2840
(2)3.6×20.1
=3.6×(20+0.1)
=3.6×20+3.6×0.1
=72+0.36
=72.36
(3)0.25×16.7-0.25×0.7
=0.25×(16.7-0.7)
=0.25×4×4
=1×4
=4
(4)12.5×(100+0.8)
=12.5×100+12.5×0.8
=1250+10
=1260
(5)4×0.8×12.5×2.5
=(4×2.5)×(0.8×12.5)
=10×10
=100
(6)(4.2×2.5)×0.4
=4.2×(2.5×0.4)
=4.2×1
=4.2
(7)0.125×32×2.5
=(0.125×8)×(4×2.5)
=1×10
=10
(8)0.8×63-8×5.3
=8×6.3-8×5.3
=8×(6.3-5.3)
=8×1
=8
(9)5.4×9.9
=5.4×(10-0.1)
=5.4×10-5.4×0.1
=54-0.54
=53.46
点评:
本题考点: 小数四则混合运算.
考点点评: 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定律简便计算.