A simple application of Bayes' Theorem will dissolve lots and lots and lots of things you fear, but irrationally. The fear du jour in light of the Boston Marathon bombing: Muslim Rage.
Undoubtedly, you probably once asked a math teacher "when am I ever gonna use this?" In light of recent developments in the investigation of Monday's bombing at the Boston Marathon, I have an answer: you'll use this when you're surrounded by demagogues calling for the waste of additional resources screening members of a minority group (if not members' outright persecution) based on the despicable actions of a small handful of people.
Here's a great post from two years or so ago in which William Easterly lampoons the statistical illiteracy of people who want to persecute or "profile" Muslims based on Muslims' role in 9/11 and other attacks and that is relevant again in light of their alleged role in the Boston bombing. The upshot: even if the probability that someone is a Muslim given that he is a terrorist is 100%--meaning that all terrorists are Muslims, which they aren't--the probability that a Muslim is a terrorist is not. In fact, the probability of a Muslim being a terrorist is, according to Easterly's calculations, 0.007% or 0.0007% (depending on which one features a typo--but even with an order-of-magnitude typo in the downward direction the probability is basically low enough to ignore).
I think a lot of people scared of Muslim Rage understand this more intuitively when we're dealing with crimes committed by white people, crimes committed with guns, and crimes committed by white people with guns. Consider school shootings. A quick Google search turned up this piece about Katherine Newman's book Rampage: The Social Roots of School Shootings. Apparently, all of the school shooters Newman studied have been white males (this article offers counterexamples, but let's just go with "all school shooters are white males" for sake of the example). Most of us understand that even if all school shooters are white males, it's a mistake to be suspicious of all white males because they might be school shooters. A lot of us also understand that even if all school shooters are gun owners, it's a mistake to be suspicious of all gun owners because they might be school shooters. Being suspicious of Muslims generally because a lot of terrorists are Muslims is the exact same mistake.
Will most people reallocate their time and energy away from reading the news and toward studying Bayes' Theorem? I doubt it: they'll remain rationally irrational and vote accordingly. Some will, though, and those who do will lead more peaceful lives as a result.