(1)( + )×15 | (2) × + ×![]() | (3) × ×![]() |
| (4)2.5×97×0.4 | (5)1.25×97×8 | (6)1.25×32×2.5×97 |
| (7)0.36×101 | (8)0.36×98 | (9) - ×![]() |
(10) + ×![]() | (11) + ×![]() | (12) - ×![]() |
(13)90×![]() | (14)86×![]() | (15) × - ×![]() |
| (16)0.36×101-0.36 | (17)0.36×99+0.36 | (18) × - . |
+
)×15,=
×15+
×15,=3+5,
=8;
(2)
×
+
×
,=(
+
)×
,=1×
,=
;(3)
×
×
,=
×
×
,=
×
,=
;(4)2.5×97×0.4,
=(2.5×0.4)×97,
=1×97,
=97;
(5)1.25×97×8,
=(1.25×8)×97,
=10×97,
=970;
(6)1.25×32×2.5×97,
=1.25×8×4×2.5×97,
=(1.25×8)×(4×2.5)×97,
=10×10×97,
=9700;
(7)0.36×101,
=0.36×(100+1),
=0.36×100+0.36×1,
=36+0.36,
=36.36;
(8)0.36×98,
=0.36×(100-2),
=0.36×100-0.36×2,
=36-0.72,
=35.28;
(9)
-
×
,=(1-
)×
,=
×
,=
;(10)
+
×
,=(1+
)×
,=
×
,=
;(11)
+
×
,=
+
,=
;(12)
-
×
,=(1-
)×
,=
×
,=
;(13)90×
,=(91-1)×
,=91×
-1×
,=4-
,=3
;(14)86×
,=(91-5)×
,=91×
-5×
,=2-
,=1
;(15)
×
-
×
,=(
-
)×
,=1×
,=
;(16)0.36×101-0.36,
=0.36×(101-1);
=0.36×100,
=36;
(17)0.36×99+0.36,
=0.36×(99+1),
=0.36×100,
=36;
(18)
×
-
,=
-
,=
.分析:(1)(2)(7)(8)(9)(10)(12)(13)(14)(15)(16)(17)运用乘法分配律简算;(3)(4)(5)运用乘法交换律简算;(6)先把32分解成8×4,再运用乘法结合律简算;(11)(18)按照先算乘除,再算加减,有括号的先算括号里面的顺序计算.
点评:运算定律是常用的简便运算的方法,要熟练掌握,灵活运用.