《2025年同步练习西南大学出版社五年级数学上册西师大版四川专版》

1. 计算。
$2.9 - 0.4×3 = $1.7 $0.025×40 = $1
$0.93 + 0.2×7 = $2.33 $4.5×99 + 4.5 = $450
$3.4×3 + 2 = $12.2 $0.125×0.8 = $0.1
$0.7 - 0.7×0.3 = $0.49 $2.7×2 - 3 = $2.4

答案： 1. $2.9 - 0.4×3$
= $2.9 - 1.2$
= $1.7$
2. $0.025×40$
= $1$
3. $0.93 + 0.2×7$
= $0.93 + 1.4$
= $2.33$
4. $4.5×99 + 4.5$
= $4.5×(99 + 1)$
= $4.5×100$
= $450$
5. $3.4×3 + 2$
= $10.2 + 2$
= $12.2$
6. $0.125×0.8$
= $0.1$
7. $0.7 - 0.7×0.3$
= $0.7×(1 - 0.3)$
= $0.7×0.7$
= $0.49$
8. $2.7×2 - 3$
= $5.4 - 3$
= $2.4$

2. 想一想,填一填。
(1)$3.84×(9.2 - 7) + 5.6$,应先算(减法),再算(乘法),最后算(加法)。
(2)$12.5×4.97×0.8$,应先算($12.5×0.8$),再算($10×4.97$),比较简便。

答案：
(1)减法，乘法，加法；
(2)$12.5×0.8$，$10×4.97$

3. 用简便方法计算。
$23.16 - 15.9 + 16.84$ $7.8×0.64 - 0.64×3.8$
$4×7.2×0.25$ $12.5×32×2.5$

答案： 1.
$23.16 - 15.9 + 16.84$
$=23.16 + 16.84 - 15.9$
$=40 - 15.9$
$=24.1$
2.
$7.8×0.64 - 0.64×3.8$
$=(7.8 - 3.8)×0.64$
$=4×0.64$
$=2.56$
3.
$4×7.2×0.25$
$=4×0.25×7.2$
$=1×7.2$
$=7.2$
4.
$12.5×32×2.5$
$=12.5×(8×4)×2.5$
$=(12.5×8)×(4×2.5)$
$=100×10$
$=1000$