- Associated Press - Wednesday, June 18, 2014

RIO DE JANEIRO (AP) - Every four years, the World Cup forces fans to remember their math lessons.

Working out what each team needs from its final match to finish in the top two of a group and advance to the knockout rounds takes some algebra knowledge and powers of prediction.

After Brazil and Mexico played to a scoreless draw on Tuesday, the calculation became clear: Both teams just need to draw in their next matches to advance with five points in Group A. Croatia, which beat Cameroon Wednesday, would get to six points by beating Mexico. So a draw with Cameroon would still get Brazil through with five points. If Mexico beats Croatia, Brazil would advance even if it loses. But if Mexico and Croatia draw, and Brazil loses - then it gets complicated with tiebreakers.

Got that, or do you need a calculator and a notepad? For most of the other teams in the tournament, the calculations are almost endless.

Three straight wins for anyone guarantees topping the standings and avoiding other group winners in the round of 16. At the 2010 World Cup, only Argentina and the Netherlands came through with a 100 percent record in the group stage.

Winning makes it easy. The Netherlands and Chile are both in with two victories worth six points. The game between them will just determine seeding for the knockout stage.

Losing makes it simple, too. Australia and Spain are eliminated after losing their first two games.

But any team in the middle risks falling into a tiebreaker to decide the qualifying positions. In that scenario, goal difference is king.

Goal difference gets to the essence of football: Score more goals than you concede. So even in the last minutes of a 3-0 game, a late goal by either side in the World Cup could decide the fate of a national team.

The simple equation is deduct how many goals a team conceded overall from how many it scored, and - ideally - what’s left is a positive number. It is effectively worth an extra point.

Think goal difference is tough to work out on the fly mid-match? Meet “goal average”.

Up to the 1966 World Cup, FIFA used goal average - a team’s total goals scored divided by goals conceded - to decide tiebreakers. Goal difference arrived in 1970.

Four years ago in South Africa, goal difference was decisive for two group winners - including the United States - who finished level on points with the runner-up.

After 90 minutes of its third match the Americans were third in the live standings. Landon Donovan’s stoppage-time winner against Algeria lifted his team top above England and Slovenia.

Runners-up in two other 2010 groups advanced by virtue of better goal difference than the third-placed team.

Story Continues →