Question 835366
Look at the possible 3 number permutations.
There are 60 total. 
123 124 125 132 134 135 142 143 145 152 153 154 
213 214 215 231 234 235 241 243 245 251 253 254 
312 314 315 321 324 325 341 342 345 351 352 354 
412 413 415 421 423 425 431 432 435 451 452 453 
512 513 514 521 523 524 531 532 534 541 542 543
The ones that contain only 3,4, and 5 are:
345 354 435 453 534 543
That's 6 out of 60.
P(3,4,5)={{{6/60=1/10}}}