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Years playing backgammon: 20+ Learned to play on fibs.com playing bots and review with gnubg analysis FIBS rating 1750-1850
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Can you count to 36? How many shots hit?

Here is an example of a -.122 blunder I made because I don't know how to count.
shots.jpg
So I am playing White and roll 6-3.
I moved 24/18 8/5

The correct move is 24/15

The error -.122 which is rated a blunder.
My winning chance was reduced from 38% to 32%.
Not good !

So why did i make this mistake?
I assumed that leaving only 1 blot was better than leaving 2 blots. So I moved 24/18 and safety the blot on the 8 pt with 8/5
So let's count the shots.

My move gets hit with any 6 and any 1 and also with the indirect shot of 11 from that back checker.
Counting shots for multiple numbers we must eliminate any duplicates.
A checker 6 away can be hit with 17/36 numbers. As we learned in a previous post, 6 is the number with the most hitting shots.
1 hits with 11/36 hitting making a total of 17+11 = 28
Take out the duplicates 6-1, 1-6, 5-1, 1-5, leaves 28-4 = 24 total hitting shots
plus the indirect 11 away shot is 2 hitting numbers whoa.. 11 is 5-6 6-5 which is duplicated so our total is still 24 shots for 6 1 and 11

Now the other option leaves 3, 1, and 8 away which also happens to be 24 shots.
3 is 14/36 rolls
1 is 11/36 rolls minus duplicates 3-1, 1-3, 2-1, 1-2 1-1 so 25-5 = 20
8 is 6 rolls minus duplicates 5-3, 3-5 =4 so 20+4
24 total hitting numbers for 8,1,3

So if both moves have the same hitting numbers, why is one a blunder?

Well we can look at what happens if we don't get hit. If we are sitting way back on the 18 pt our chances of clearing that back checker are not so good.
If on the other hand we are at the 15 pt and the opponent misses, we are looking much better. Also if the opponent miss we have a chance to hit with our 1 and better chances to hit with the 8 away checker. Opponent cant safety that checker because of the big racing lead we have so they are not looking to break contact. So our chances are way better when we move to the 15 pt. If we sit on the 18 point, our opponent has nothing to worry about with the blot on our 7 pt and they will get another chance to hit as we are not likely to clear that back checker on the next turn.

An expert player will look at a position like this and they will think about it for a while before moving. They will see the shots are equal so then they will consider what position they want to be in if the opponent misses. And they will make the correct play. A bigger blunder is not to move up the back checker with the 6. -.168 blunder. Winning chance reduced from 38% down to 30% if you don't move the back checker.

1. Cubeful 3-ply 24/15 Eq.: -0.218
0.388 0.061 0.001 - 0.612 0.084 0.003
3-ply cubeful
2. Cubeful 3-ply 24/18 8/5 Eq.: -0.340 ( -0.122)
0.327 0.059 0.001 - 0.673 0.038 0.001
3-ply cubeful
3. Cubeful 2-ply 24/18 4/1 Eq.: -0.287 ( -0.069)
0.351 0.093 0.002 - 0.649 0.114 0.005
2-ply cubeful
4. Cubeful 2-ply 24/18 5/2 Eq.: -0.298 ( -0.081)
0.346 0.086 0.002 - 0.654 0.121 0.005
2-ply cubeful
5. Cubeful 2-ply 24/18 6/3 Eq.: -0.320 ( -0.102)
0.336 0.067 0.002 - 0.664 0.120 0.004
2-ply cubeful
6. Cubeful 2-ply 8/2 5/2 Eq.: -0.386 ( -0.168)
0.304 0.055 0.001 - 0.696 0.029 0.001
2-ply cubeful
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