Position 66, page 120
From Backgammon for Blood, by Bruce Becker

White to play 6-2.

You bear off one man from your 5 point and then you must move the 2. Most players I’ve seen, when in a situation like this, would move from the higher point: that is, they would move the man remaining on W5 to W3. Since Black will certainly remove two of his men on his next throw (assuming he doesn’t throw doubles) and then will bear off his last two men on his next throw, you can win only by getting both your men off on your next throw. So, the question here is whether you made the best move possible for your 6-2 throw. The answer is no.

You had no choice about bearing off one of the men on W5 for the 6 move, but instead of moving the other W5 man to W3, leaving you with men on the 3 and 4 points, you should have moved the man on W4 to W2, leaving you with men on the 2 and 5 points. This is because with a 2 and 5 position you have more than a 50–50 chance to get both men off in one throw. Any position better than this will simply be that much surer of winning, and any position worse than this brings your chance of winning below the 50–50 mark. And that is why 2-5 is the magical number.

The 2-5 combination is crucial for this purpose, and you cannot trifle with it. That is, you cannot think that a 1-6 or a 3-4 are as good because they also total 7 — which is the way some people count: by totals. Here, the total is not critical, but the fact that one man must be on the 2 point (or better), and the other man must be on the 5 point (or better), if you want to have at least a 50 percent chance to bear off in one throw.

Consequently, and especially in a close race, when it is getting down to the wire, 2-5 is what you should aim for.

Should you have a slightly better position that this, remember that the 5 is more sensitive than the 2. That is, move the man from the 2 point to the 1 point before moving the man on the 5 point to the 4 point. Although there are the same number of ways to bear off a 1-5 position and a 2-4 position (twenty-three), you are considerably better with a 1-4 position (twenty-nine ways) than with a 2-3 position (twenty-five ways).

And for a position that is slightly worse than the 2-5, the rule is the same: play with the two before you disturb the five. For example, you are better with a 3-5 position (fourteen ways) than a 2-6 position (thirteen ways).

5/off, 4/2  *
Not: 5/off, 5/3
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Tom Keith 2013 
Money play
Centered cube
White rolls 6-2

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6-2: Game BG   Equity
1 5/off, 4/2 W
−0.0864 x  *
2 5/3, 5/off W
−0.3735 (0.2871)  Not

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List of Positions from Backgammon for Blood

Backgammon for Blood (1974), by Bruce Becker

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