Okay, so I think I have this worked out now, If you take each combo of points (assuming the public vote is graded in the same way as the judges vote)

Possible scenarios!

Rachel = 3 +1 = 4
Lisa = 3 + 2 = 5
Tom = 1 + 3 = 4

Tom and Rachel in dance off

Rachel = 3 + 3 = 6
Lisa = 3 + 2 = 5
Tom = 1 + 1= 2

Tom and Lisa in dance off

Rachel = 3 + 1 = 4
Lisa = 3 + 3 = 6
Tom = 1 + 2= 3

Tom and Rachel in dance off

Rachel = 3 + 3 = 6
Lisa = 3 + 1 = 4
Tom = 1 + 2= 3

Tom and Lisa in dance off

Rachel = 3 + 2 = 5
Lisa = 3 + 3 = 6
Tom = 1 + 1= 2

Rachel and Tom in dance off

Rachel = 3 + 2 = 5
Lisa = 3 + 1 = 4
Tom = 1 + 3 = 4

Lisa and Tom in dance off



So, with any possible combination of points, Tom would automatically be in the dance off as he would never be able to get enough points to beat the other two.

sorry for the long post, I think I have it worked out now tho!

But really, given that it appears to be pretty common knowledge that Tom attracts significantly more votes than the women, the Final is now Tom's and the whole thing is a foregone conconclusion.