解题思路:(1)利用乘法交换律和结合律先计算0.8×1.25,再与3.9相乘;
(2)利用乘法分配律的逆运算进行简便计算;
(3)把9.9写成10-0.1,再利用乘法分配律计算即可解答;
(4)根据连减的性质:a-b-c=a-(c+b)进行简便计算即可解答;
(5)把3.2写成0.4×8,再把2.5和0.4相乘,8和12.5相乘,再把所得的积相乘即可;
(6)此题没有简便计算的方法,按照运算顺序,先算乘法,再算加法,计算即可.
(1)0.8×3.9×1.25
=0.8×1.25×3.9
=1×3.9
=3.9
(2)4.87×2.34+4.87×7.66
=4.87×(2.34+7.66)
=4.87×10
=48.7
(3)0.49×9.9
=0.49×(10-0.1)
=0.49×10-0.49×0.1
=4.9-0.049
=4.851
(4)60.8-7.18-12.82
=60.8-(7.18+12.82)
=60.8-20
=40.8
(5)2.5×3.2×12.5
=2.5×(0.4×8)×12.5
=(2.5×0.4)×(8×12.5)
=1×100
=100
(6)3.95×7.6+2.4
=30.02+2.4
=32.42.
点评:
本题考点: 小数四则混合运算;运算定律与简便运算.
考点点评: 完成本题要注意分析式中数据,运用合适的简便方法计算.