Someone like JFC would be able to confirm this but as far as i am aware the answer would go along the lines of this:

Favourite: 57%
Underdog: 43%

0 favourites winning: 0.43*0.43*0.43 = 7.95%
1 favourites winning: 0.57*0.43*0.43 = 10.5%
2 favourites winning: 0.57*0.57*0.43 = 13.97%
3 favourites winning: 0.57*0.57*0.57 = 18.51%

Think that's correct.

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I like Bing Lee.