What is Probability?

Thisweekend my friends and I played a board game called Stone Age, where you hunt,collect resources and construct buildings. During the game, a player drew a card that called for rolling dice todetermine what resources we'd get.  Hewanted to roll a '6' because that meant he'd get a valuable farm, and so wetalked about the odds of rolling a '6' with four dice.
Thisleads us to probability.  Probability issimply the measure of how likely something is to happen.  It can be a small thing, like the flip of acoin, or something big, like the likelihood you'll get into a car wreck. 
Aprobability can be expressed as a fraction between 0 and 1, or as a percentageof 0% to 100%.  In our daily lives, wemay not take the time to write down the exact fractions or percentages, but wemake educated guesses all the time.
Ifyou're choosing what route to take home from work and you know it's the Fridaybefore a three-day weekend, you'll predict what highways or bridges will be jammed,and then choose a different road.  Ifyou're in an office pool for the NCAA basketball tournament, you'll figure somerough probabilities in your head as you pick your bracket winners.
Wedo this stuff all the time, so we shouldn't let the math part scare us.
Sincethe 1500s, mathematicians and gamblers have studied probability.  Famous thinkers like Fermat and Pascalexamined this topic, and there has long been a connection between betting andmath.  Even the phrase "games ofchance" tells us they involve probability. One of the early papers on probability, titled "Doctrine ofChances" by DeMoivre, contained problems which calculated the odds ofwinning lottery tickets.
Oneodd branch of this area is actuarial science, where insurance actuaries usemath and statistics to make probability predictions about all sorts of things,including death.  An early example ofthis is the London Life Table created by John Graunt in the 1600s.  Graunt used the lifespans of 100 people inthe city and noted how long they lived, which provided useful data about theappalling mortality rate among children of that era.
Ifyou're curious how many more years you may live, follow this link to a SocialSecurity chart.  The chart does not takeinto account where you live, or if you're in a dangerous occupation, etc., soit is quite broad.  But you can look atyour gender, figure out what age you were in 2007 (when the chart was made),and then look at the column labeled "Life Expectancy" and see howmany more years you may live.  It issobering. 
Anda reminder that you should use well the days you have on this Earth.  
(Sources include:  Education World, an article by Amy Troutmanat Wichita.edu, and Social Security Online. The pic is from Google Images.)