Position 39c, page 120
From The Backgammon Book, by Oswald Jacoby and John R. Crawford

Should White
double to 2?

Let’s begin by calculating your chance to win if the game is played to the end. You will win if you get off in one roll, or if you get a second roll and get off then.

Table 4 shows that your total chance of getting off in two rolls is 78 per cent, and of getting off in one roll 11 per cent. Hence, your chance of getting off on your second roll is the difference, or 67 per cent. However, you may not get a second roll. Your opponent has one chance in six (six possible rolls out of thirty-six) of rolling a double and winning before you get that second roll. Therefore, your chance to win is 11 per cent plus 5/6 of 67 per cent. This adds up to 67 per cent.

A probability of 67 per cent is equivalent to odds of about two to one in your favor, and so you should double or redouble, as the case may be. You may wish you hadn’t redoubled if you proceed to roll 2-1 and get redoubled right back, but you should not let this possibility dissuade you.

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List of Positions from The Backgammon Book

The Backgammon Book (1970), by Oswald Jacoby and John R. Crawford