Question

18．脱式计算，能简算的要简算．

0.25×1.25×3.2	0.45×99+0.45	0.65×20.1
8.715÷0.83-2.9	7.28+3.2÷2.5	0.75×18÷0.15．

Answer 1

分析 ①把3.2看作8×0.4，再运用乘法结合律计算，即（1.25×8）×（0.25×0.4）．
②、③用乘法分配律计算即可．
④先算除法算式，再算减法算式即可．
⑤先算除法算式．再算加法算式．
⑥先算0.75除以0.15得5．再算18乘5即可．

解答 解：①0.25×1.25×3.2
=0.25×1.25×8×0.4
=（1.25×8）×（0.4×0.25）
=10×0.1
=1

②0.45×99+0.45
=0.45×（99+1）
=0.45×100
=45

③0.65×20.1
=0.65×（20+0.1）
=0.65×20+0.1×0.65
=13+0.065
=13.065

④8.715÷0.83-2.9
=10.5-2.9
=7.6

⑤7.28+3.2÷2.5
=7.28+1.28
=8.56

⑥0.75×18÷0.15
=0.75÷0.15×18
=5×18
=90

点评 此题考查了学生对小数四则混合运算题的计算能力，以及灵活巧算的能力．