How many integers between 100 and 500 have at least two 3s as digits?
13 = 133, 233, 330, 331, 332, 333, 334, 335, 336, 337, 338, 339, 433.
There are actually 22 of them:
133 , 233 , 303 , 313 , 323 , 330 , 331 , 332 , 333 , 334 , 335 , 336 , 337 , 338 , 339 , 343 , 353 , 363 , 373 , 383 , 393 , 433 , Total = 22
