## A Gentle Introduction to Probability

**Sisters’ Dilemma: Who’s going to grandma?**

Issa and Ishi go to their grandmother every weekend. Next weekend, however, their mother will be leaving for an important errand, so one of them has to stay home. Both sisters wanted to go, so to decide, they agreed on a toss coin. If the result is head, then Issa will go, if tail, Ishi will.

Tossing a coin would only result to two possible *outcomes*: a head or a tail. Assuming that the coin is fair, the chance of Issa winning the toss coin is 1 out of 2, or 50 percent. From the context, intuition tells us that the chance of Issa winning is the ratio of the number of outcomes favorable to her (that is getting a head) to the total number of possible outcomes (head and tail). Obviously, Ishi has the same chance of winning. » Read more