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©2026 数学クラブ http://sugaku.club/
月 日（ ）
● 次の計算をしなさい
[1C1-00]
(1)
81
×
79
(2)
27
×
33
(3)
102
×
98
(4)
2
58
(5)
91
×
89
(6)
2
39
(7)
89
×
91
(8)
2
33
(9)
2
61
(10)
2
47
(11)
2
42
(12)
2
38
©2026 数学クラブ http://sugaku.club/
月 日（ ）
【解答例】
(1)
81
×
79
2
2
=
(
80
＋
1
)
(
80
−
1
)
=
80
−
1
=
6400
−
1
=
6399
(2)
27
×
33
2
2
=
(
30
−
3
)
(
30
＋
3
)
=
30
−
3
=
900
−
9
=
891
(3)
102
×
98
2
2
=
(
100
＋
2
)
(
100
−
2
)
=
100
−
2
=
10000
−
4
=
9996
(4)
2
58
2
2
2
=
(
60
−
2
)
=
60
−
2
×
60
×
2
＋
2
=
3600
−
240
＋
4
=
3364
(5)
91
×
89
2
2
=
(
90
＋
1
)
(
90
−
1
)
=
90
−
1
=
8100
−
1
=
8099
(6)
2
39
2
2
2
=
(
40
−
1
)
=
40
−
2
×
40
×
1
＋
1
=
1600
−
80
＋
1
=
1521
(7)
89
×
91
2
2
=
(
90
−
1
)
(
90
＋
1
)
=
90
−
1
=
8100
−
1
=
8099
(8)
2
33
2
2
2
=
(
30
＋
3
)
=
30
＋
2
×
30
×
3
＋
3
=
900
＋
180
＋
9
=
1089
(9)
2
61
2
2
2
=
(
60
＋
1
)
=
60
＋
2
×
60
×
1
＋
1
=
3600
＋
120
＋
1
=
3721
(10)
2
47
2
2
2
=
(
50
−
3
)
=
50
−
2
×
50
×
3
＋
3
=
2500
−
300
＋
9
=
2209
(11)
2
42
2
2
2
=
(
40
＋
2
)
=
40
＋
2
×
40
×
2
＋
2
=
1600
＋
160
＋
4
=
1764
(12)
2
38
2
2
2
=
(
40
−
2
)
=
40
−
2
×
40
×
2
＋
2
=
1600
−
160
＋
4
=
1444