Ask The Wizard #186
However, sometimes free slot play must be done on particular promotional machines that don’t accept money. The value of this kind of free play is hard to estimate closely, but generally very little. For example, the Las Vegas World used to sell “$1000” vacation packages for $400. Of the alleged $1000 value $600 was in promotional slot machine play. In his book “Million Dollar Video Poker,” Bob Dancer writes that he did this deal numerous times over, and estimates the value of the free slot play to be about ten cents on the dollar.
The probability that these five ranks will represent three suits, two of two, and one of one, is combin(4,2)*2*combin(5,2)*combin(3,2)=360. Combin(4,2) is the number of ways to choose two suits out of four for the suits represented twice. 2 for the two ways to choose the suit represented once. Combin(5,2) for the number of ways to choose two ranks out of five for the first suit of two cards. 45 for the number of ways to choose two ranks out of the three left for the other suit of two.
The probability these five ranks will represent four suits, one of two, and three of one, is 4*combin(5,2)*3*2=240. 4 is the number of ways to choose one suit out of four for the suits represented twice. Combin(5,2) is the number of ways to choose two ranks out of five for that suit of two cards. 3 is the number of ways to choose one rank out of the three left for the first suit of one. 2 is the number of ways to choose one rank out of two for the second suit of one.
There are 45=1024 ways to arrange four suits on five different ranks.
So the probability that no more than two of one suit will be present is (360+240)/1024 = 600/1024 = 58.59%.
There are combin(13,5)=1287 ways to arrange 5 ranks out of 13. The number of these combinations in which no three ranks are within a span of 5 is 79. There is no easy formula for this one. I had to cycle through every combination. So the probability the ranks will be sufficiently spaced apart is 79/1287 = 6.14%.
So, the probability of a broken board is (1317888/2596960)*(600/1024)*(79/1287) = 1.825211%.
I have been challenged on my number of broken straights. Here is a list of all 79 possible.
| 2378Q 2378K 2379Q 2379K 237TQ 237TK 237JQ 237JK 237QK 2389K 238TK 238JK 238QK 2479Q 2479K 247TQ 247TK 247JQ 247JK 247QK | 2489K 248TK 248JK 248QK 257TQ 257TK 257JQ 257JK 257QK 258TK 258JK 258QK 267JQ 267JK 267JA 267QK 267QA 267KA 268JK 268JA | 268QK 268QA 268KA 269JA 269QA 269KA 278QK 278QA 278KA 279QA 279KA 289KA 3489K 348TK 348JK 348QK 358TK 358JK 358QK 368JK | 368JA 368QK 368QA 368KA 369JA 369QA 369KA 378QK 378QA 378KA 379QA 379KA 389KA 469JA 469QA 469KA 479QA 479KA 489KA |