题目内容
简算
①9
-(3
+0.4)
②1.8×
+2.2×25%
③
+
+
+…+
+
.
①9
| 2 |
| 5 |
| 3 |
| 7 |
②1.8×
| 1 |
| 4 |
③
| 1 |
| 1×3 |
| 1 |
| 3×5 |
| 1 |
| 5×7 |
| 1 |
| 17×19 |
| 1 |
| 19×21 |
①9
-(3
+0.4),
=9
-3
-
,
=9
-
-3
,
=9-3
,
=5
;
②1.8×
+2.2×25%,
=1.8×0.25+2.2×0.25,
=(1.8+2.2)×0.25,
=4×0.25,
=1;
③
+
+
+…+
+
,
=
×(1-
)+
×(
-
)+…+
×(
-
)+
×(
-
),
=
×(1-
+
-
+…+
-
+
-
),
=
×(1-
),
=
×
,
=
.
| 2 |
| 5 |
| 3 |
| 7 |
=9
| 2 |
| 5 |
| 3 |
| 7 |
| 2 |
| 5 |
=9
| 2 |
| 5 |
| 2 |
| 5 |
| 3 |
| 7 |
=9-3
| 3 |
| 7 |
=5
| 4 |
| 7 |
②1.8×
| 1 |
| 4 |
=1.8×0.25+2.2×0.25,
=(1.8+2.2)×0.25,
=4×0.25,
=1;
③
| 1 |
| 1×3 |
| 1 |
| 3×5 |
| 1 |
| 5×7 |
| 1 |
| 17×19 |
| 1 |
| 19×21 |
=
| 1 |
| 2 |
| 1 |
| 3 |
| 1 |
| 2 |
| 1 |
| 3 |
| 1 |
| 5 |
| 1 |
| 2 |
| 1 |
| 17 |
| 1 |
| 19 |
| 1 |
| 2 |
| 1 |
| 19 |
| 1 |
| 21 |
=
| 1 |
| 2 |
| 1 |
| 3 |
| 1 |
| 3 |
| 1 |
| 5 |
| 1 |
| 17 |
| 1 |
| 19 |
| 1 |
| 19 |
| 1 |
| 21 |
=
| 1 |
| 2 |
| 1 |
| 21 |
=
| 1 |
| 2 |
| 20 |
| 21 |
=
| 10 |
| 21 |
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