Help calculating Exactas Needed
 

Supposing a Race had 8 Runners.
And I calculated the Percentage Chances of the animals of winning.
And I also calculated the Percentage Chances of the animals running second.

How can I use these Percentage Chances to Calculate Exactas?
When I simply Mutiply them , I get situations where an animal can't run both First and Second.
And If I simply eliminate these impossible permutations, then the sum of all the other combinations adds up to only 80% instead of 100%

Heres the Numbers I used.

Tab Numbers - Win Percentage - 2nd place Percentage.

1 10.1% 12.8%
2 30.3% 18%
3 19% 24.1%
4 2.8% 3.6%
5 2.1% 2.7%
6 6.1% 7.7%
7 6.1% 7.8%
8 23.4% 23.3%

I won't say this is the most accurate method but multiply the first price x second price then mutiply by 1.3