Jenson can wrap it up this weekend in Brazil

Get out the calculator.

Title leader Jenson Button lines up for the penultimate world championship round in Brazil with 85 points to his name.

The only other drivers in contention are his Williams-bound Brawn team-mate Rubens Barrichello (71), Sebastian Vettel of Red Bull Racing (69).

With only 20 points up for grabs in total in Brazil and Valencia, Button can seal the deal if he takes third or better on Sunday, regardless of whether his rivals win or not.

Third will give Button 91 points, meaning that he'll be world champ even is Barrichello banked 20 points from two victories in the last two races. (Remember that Button needs only to accumulate the same number of points as anyone else because he has won more races and would take the title on a countback.)

Still with me?

Other scenarios are many and varied this weekend.

Button will still be world champ if Barrichello doesn't win and Button finishes fourth or fifth.

Button can afford to finish sixth or seventh provided Barrichello claims no higher than third and Vettel no higher than second.

If Button takes one point from eighth, the title is his if Barrichello finishes fourth or lower, with Vettel no better than third.

And Button will win by not adding to his tally at Interlagos, if Vettel does no better than third and the boy from Brazil finishes fifth or worse.

Disclaimer: Maths was not my strong suite at school...