インド式の掛け算では9よりも大きい数どうしの掛け算も暗算で計算します。特に11から19までの掛け算は算数でも数学でもよく出てきます。下の表は11×11から19×19までの掛け算です。
11 × 11 = 121
11 × 12 = 132
11 × 13 = 143
11 × 14 = 154
11 × 15 = 165
11 × 16 = 176
11 × 17 = 187
11 × 18 = 198
11 × 19 = 209
12 × 11 = 132
12 × 12 = 144
12 × 13 = 156
12 × 14 = 168
12 × 15 = 180
12 × 16 = 192
12 × 17 = 204
12 × 18 = 216
12 × 19 = 228
13 × 11 = 143
13 × 12 = 156
13 × 13 = 169
13 × 14 = 182
13 × 15 = 195
13 × 16 = 208
13 × 17 = 221
13 × 18 = 234
13 × 19 = 247
14 × 11 = 154
14 × 12 = 168
14 × 13 = 182
14 × 14 = 196
14 × 15 = 210
14 × 16 = 224
14 × 17 = 238
14 × 18 = 252
14 × 19 = 266
15 × 11 = 165
15 × 12 = 180
15 × 13 = 195
15 × 14 = 210
15 × 15 = 225
15 × 16 = 240
15 × 17 = 255
15 × 18 = 270
15 × 19 = 285
16 × 11 = 176
16 × 12 = 192
16 × 13 = 208
16 × 14 = 224
16 × 15 = 240
16 × 16 = 256
16 × 17 = 272
16 × 18 = 288
16 × 19 = 304
17 × 11 = 187
17 × 12 = 204
17 × 13 = 221
17 × 14 = 238
17 × 15 = 255
17 × 16 = 272
17 × 17 = 289
17 × 18 = 306
17 × 19 = 323
18 × 11 = 198
18 × 12 = 216
18 × 13 = 234
18 × 14 = 252
18 × 15 = 270
18 × 16 = 288
18 × 17 = 306
18 × 18 = 324
18 × 19 = 342
19 × 11 = 209
19 × 12 = 228
19 × 13 = 247
19 × 14 = 266
19 × 15 = 285
19 × 16 = 304
19 × 17 = 323
19 × 18 = 342
19 × 19 = 361
平方数
同じ数をかけた掛け算だけ取り出してみましょう。
11 × 11 = 121
12 × 12 = 144
13 × 13 = 169
14 × 14 = 196
15 × 15 = 225
16 × 16 = 256
17 × 17 = 289
18 × 18 = 324
19 × 19 = 361
