Trifectas are frustrating.

Heres an angle that has a low out going with reasonable results.
Using the pre-post market in the newspaper.

Back either the first or second fav. to win and leave the other out all together .

Then back the 3rd.4th.5th.6th&7th Fav. to run 2nd.& 3rd.
So it will look like this
1st.or 2nd Fav to win(leaving one out) with 3-7th Favs. to run 2nd.& 3rd.
Cost $20 outlay for a $1.00 unit

If horses are sharing the same price line in the newspaper. Take them in numerical TAB order.E.g. if TAB Nos.1,2,3 are all on the 3rd. line of betting , they now become selections 3,4,5 to run 2nd. & 3rd.

If there are 2 horses sharing favortisim, the are treated as being 1st.& 2nd. Favorite.
You now have to delete one of them alltogether. Because they very rarely get up to gether in the same trifecta.

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Cheers.