In a dart game, Jessie hit the bulls-eye on 15 of 20 throws. Based on these results, what are the odds in favor of her hitting the bullseye on her next throw? Answer is 3 to 1, why?

prob of heading bull's eye = 15/20 = 3/4

So the prob of not heading it is 1/4

odds in favour of some event = prob(of event) : prob(not the event)
= (3/4) : (1:4)
= 3:1