# Math professor teaches street fighting at MIT

When in doubt, applying street fighting tactics in the classroom can help students learn, says Dr. Sanjoy Mahajan.

Street fighting and self-defense require quick thinking and an ability to “shoot first and ask questions later.” These ninja skills also apply to students in Dr. Sanjoy Mahajan’s class based on his book, “Street-Fighting Mathematics.”

For his class, available to MIT and Massive Open Online Courses students with basic physics and algebra comprehension, Mahajan says he doesn’t want his students to “wait for the perfect kick to come” — he encourages them to just go for it.

The lessons seek to rid students of math anxieties by emphasizing the art of problem-solving without doing an exact, lengthy calculation. “They think, ‘If I don’t get this one right answer, I have nothing,’” he says. The answer itself isn’t the end-all, be-all though. That’s because in his class, a grade is not based on correct or incorrect answers; instead, it’s all about whether they’ve made a decent effort to find the answer.

By showing students an equation as they stare at various symbols in fear, he tells them not to worry, since the answer will be found differently from how they expect it to be anyhow. “The paranoia will freeze them up and just like in a street fight, they’ll get slaughtered.” In order to become liberated, he focuses on action in doing something reasonable and reacting without overthinking a solution — in other words, estimating.

The class challenges the idea that math is supposed to be exact, as students toss away the notion of perfection and right and wrong. To drive home the ninja math technique, he often uses Navier-Stokes equations, considered some of the most complex math equations out there. He says it literally takes years to solve these problems, but “to hell with that, that’s not a street-fighting approach.” With a long, arduous approach, he says problems will not be solved and suggests the street-fighting approach as a way to make progress.

Students inevitably apply the ninja method to other classes as well, Mahajan points out. Approximating helps them simplify, he explains: “When the going gets tough, lower your standards.”

Mahajan used the technique to learn German, for example. The language has endings with seven different forms of the word “the.” Instead of figuring out the proper word endings, the professor went with the most common one. “I was willing to approximate and not get ‘paralysis by analysis,’” he says. Coupled with approximating by slurring the ends of words, locals understood Mahajan based on what their ear was trained to hear. It turns out that the street fighting technique works in German, too.

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