5-2 + = | (12.5+ )×8= | 19-3 -4 = | 8+0.1÷0.1-8= |
| 21-2.897= | 0.25×0.12= | 3.6÷25%×4= | = |
+
,=2

,=3
;(2)(12.5+
)×8,=12.5×8+
×8,=100+6,
=106;
(3)19-3
-4
,=19-(3
+4
),=19-8,
=11;
(4)8+0.1÷0.1-8,
=8+1-8,
=1;
(5)21-2.897,
=21-3+0.103,
=18+0.103,
=18.103;
(6)0.25×0.12,
=0.25×(4×0.03),
=(0.25×4)×0.03,
=1×0.03,
=0.03;
(7)3.6÷25%×4,
=14.4×4,
=57.6;
(8)
,=
÷
,=
.分析:(1)按照从左到右的顺序计算;
(2)运用乘法分配律简算;
(3)根据连续减去两个数等于减去这两个数的和简算;
(4)先算除法,再算加法,最后算减法;
(5)先把减2.897看成减3再加0.103简算;
(6)先把0.12分解成4×0.03,再运用乘法结合律简算;
(7)先算除法,再算乘法;
(8)先算加法,再算除法;
点评:此题是考查四则混合运算,要仔细观察算式的特点,灵活运用一些定律进行简便计算.