题目内容

102×98
82×78
30.2×29.8
10
4
5
×9
1
5
102×98,
=(100+2)×(100-2),
=1002-22
=10000-4,
=9996;

82×78,
=(80+2)×(80-2),
=802-22
=6400-4,
=6396;

30.2×29.8,
=(30+0.2)×(30-0.2),
=302-0.22
=900-0.04,
=899.96;

10
4
5
×9
1
5

=(10+
4
5
)×(10-
4
5
),
=102-(
4
5
2
=100-
16
25

=99
9
25
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