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(2010•泸西县模拟)怎样算简便就怎样算.①8×0.4×12.5×25%②(27+15)×7×5③11998×1997+11998④197×9798+198.

题目详情
(2010•泸西县模拟)
怎样算简便就怎样算.
①8×0.4×12.5×25%
(
2
7
+
1
5
)×7×5
1
1998
×1997+
1
1998
④197×
97
98
+
1
98
▼优质解答
答案和解析
①8×0.4×12.5×25%,
=(8×12.5)×(0.4×25%),
=100×0.1,
=10;

(
2
7
+
1
5
)×7×5,
=(
2
7
+
1
5
)×(7×5),
=
2
7
×(7×5)+
1
5
×(7×5),
=(
2
7
×7)×5+(
1
5
×5)×7,
=2×5+1×7,
=10+7,
=17;

1
1998
×1997+
1
1998

=
1
1998
×(1997+1),
=
1
1998
×1998,
=1;

④197×
97
98
+
1
98

=197×(1-
1
98
)+
1
98

=197×1-197×
1
98
+
1
98

=197-
197
98
+
1
98

=197-(
197
98
-
1
98
),
=197-2,
=195.
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