How do you guys work out the expected quinella div from the win prices? I'll show you how I would do it and although it's a bit involved and not perfect I think it would give a good figure.

Say we have a four horse race and I'll keep the market percentage to 100% for simplicity.
Horse 1 is at $2.00 so it has a 50% chance (based on the prices).
Horse 2 is at $5.00 so it has a 20% chance.
Horse 3 is at $4.00 so it has a 25% chance.
Horse 4 is at $20.00 so it has a 5% chance.

To get the quinella on 1 and 2:
Chance of horse 1 winning is 50% leaving horses 2, 3, and 4 to fight out second. I'll now convert the total of their percentages to 100%. I do this by multiplying their original percentage by 100 / (100 - the %age removed)
Horse 2 has 40% ---- 20% x (100 / (100 - 50))
Horse 3 has 50%
Horse 4 has 10%
therefore horse 2 has a 40% chance of coming second.
Combining Horse 1's 50% chance of winning with horse 2's 40% chance of coming second I get (50% x 40%) = 20%.
This means there is a 20% chance of a 1 2 result, (converted back to a 100% market gives me $5 as the value of this exacta).

Now doing the same for a 2 1 result I get the original 20% chance of horse 2 winning and with the same dodgy manipulation of numbers as above I get a 62.5% chance of horse 1 beating the other two. Combine the 20% with the 62.5% and I get a 12.5% chance of a 2 1 result (this gives me a price of $8 for this exacta).

For the quinella I add these two percentage chances together. 20% + 12.5% gives 32.5% chance of getting the quinella. This equates to about $3.08 as an effective quinella price in a 100% market.

I'd be interested to see what price you guys would give for the 1 2 quinella in my example.

KV