False Key Probability

False Keys in McDowell’s Blackjack Ace Prediction

by S. Yama
(From Blackjack Forum XXIV #2, Spring 2005)
© 2005 Blackjack Forum

Radar, great rebuttal articles on McDowell’s numbers in Blackjack Ace Prediction. You wrote:

This is wrong because a share of the broken sequences and false keys properly belong to the aces that land on the other betting spots.

By subtracting .15 and .10 (.25) from .38 he comes up with an estimated 13% hit rate on his ace bets.

Instead, he should have multiplied .38 by .25.

.38 x .25 = .095

Then, he should have subtracted .095 from .38.

.38 – .095 = .285

It is a small point, however, unless I am missing something (which happens more often than I dare to admit), false key cards and broken sequences are not mutually exclusive. So it should be the chance of the Ace hitting the money minus when the sequence is broken minus when a false key card falls that is not in a broken sequence.

Or the same thing in reversed order: chance of hitting minus false card minus broken sequence without false key card. I don’t think it is a simple function of additions.

The numbers for cited case would be:

.38 – [.38 x .15 + (.38 – .38 x .15) x .1)] = .38 – .057 – .0323 = .2907 or

.38 – [.38 x .1 + (.38 – .38 x .15) x .15] = .2907

The difference is very small but I thought that you should be aware of it

S. Yama

Radar O’Reilly Replies:

Of course you’re right , S. Yama. Thanks. ♠