A counting number is called a “three-digit arrow” if its tens digit is larger than both the hundreds digit and the units digit, and the sum of the hundreds digit and the units digit. .How many three-digit arrows are there?
120 130 131 140 141 142 150 151 152 153 160 161 162 163 164 170 171 172 173 174 175 180 181 182 183 184 185 186 190 191 192 193 194 195 196 197 230 240 241 250 251 252 260 261 262 263 270 271 272 273 274 280 281 282 283 284 285 290 291 292 293 294 295 296 340 350 351 360 361 362 370 371 372 373 380 381 382 383 384 390 391 392 393 394 395 450 460 461 470 471 472 480 481 482 483 490 491 492 493 494 560 570 571 580 581 582 590 591 592 593 670 680 681 690 691 692 780 790 791 890 Total = 120 such numbers
