How many 3-digit numbers contain exactly one 1 and one 2? Examples don't include 510 and 771.
102 , 120 , 123 , 124 , 125 , 126 , 127 , 128 , 129 , 132 , 142 , 152 , 162 , 172 , 182 , 192 , 201 , 210 , 213 , 214 , 215 , 216 , 217 , 218 , 219 , 231 , 241 , 251 , 261 , 271 , 281 , 291 , 312 , 321 , 412 , 421 , 512 , 521 , 612 , 621 , 712 , 721 , 812 , 821 , 912 , 921 , >>Total permutations = 46 with one 1 and one 2.
102 , 120 , 123 , 124 , 125 , 126 , 127 , 128 , 129 , 132 , 142 , 152 , 162 , 172 , 182 , 192 , 201 , 210 , 213 , 214 , 215 , 216 , 217 , 218 , 219 , 231 , 241 , 251 , 261 , 271 , 281 , 291 , 312 , 321 , 412 , 421 , 512 , 521 , 612 , 621 , 712 , 721 , 812 , 821 , 912 , 921 , >>Total permutations = 46 with one 1 and one 2.
