PDA

View Full Version : Back Door Strait

DJSirMatthew
02-06-2005, 12:32 PM
I'm sure that this is obvious to some of you math masters out there, But I was wondering what the odds of catching your backdoor strait in hold'em. Thanks in advance...
jason_t
02-06-2005, 01:02 PM
It depends on the type of backdoor straight you have.

If you have three connected cards (say you hold J9 and the flop is Txx), the answer is

(8/47) * (8/46) + (8/47) * (4/46) = .044

the first term is the from the times you catch an open-ended straight draw on the turn and the second is from the times you catch a gutshot on the turn. this answer is correct unless you have specificially 234 or QJK in which case the answer is

(4 / 47) * (8 / 46) + (4 / 47) * (4 / 46) = 0.022

if you have a gap such a 89T the answer is

(4 / 47) * (8 / 46) = .015

if have a two gapper such as 89Q or 579 (also A23 and QKA)

the answer is

(4 / 47) * (4 / 46) = .007
binions
02-06-2005, 01:28 PM
[ QUOTE ]
It depends on the type of backdoor straight you have.

If you have three connected cards (say you hold J9 and the flop is Txx), the answer is

(8/47) * (8/46) + (8/47) * (4/46) = .044



[/ QUOTE ]

Hmmm. 4.4% with 2 cards to come? Sounds like a 3 straight is worth 1 out to me . . .
BugsBunny
02-07-2005, 03:05 PM
[ QUOTE ]
. . .
if you have a gap such a 89T the answer is

(4 / 47) * (8 / 46) = .015

if have a two gapper such as 89Q or 579 (also A23 and QKA)

the answer is

(4 / 47) * (4 / 46) = .007

[/ QUOTE ]

a 2 gapper is actually 8/47 * 4/46 = .01480
and a 1 gapper is (8/47)*(4/46)+(4/47)*(8/46) = .0296
BugsBunny
02-07-2005, 03:15 PM
A 3 straight will come in slightly more aften than a backdoor flush, but you're also more subject to losing due to someone having a higher straight, depending on the exact cards you hold and the exact turn and river.

You hold 78, flop is 9xx, you get TJ on the turn and river, you lose to 8Q or QK is just one example.

That said counting a 3 straight as 1 additional out is probably accurate. Just be aware of the possibilities that are out there. I'll usually figure a 3 straight as 1 additional out and a 1 gapper as .5 outs. A 2 gapper is just a bonus if that comes in, I don't add any outs for it.
jason_t
02-07-2005, 07:18 PM
yes, my bad. thank you.