Bring Your Questions for the Street-Fighting Mathematician


How many Starbucks are in New York City? How many light bulbs on one city block? How many airplanes are approaching Chicago O’Hare Airport right now?

This sort of question, particularly familiar to anyone who has ever interviewed for a management-consulting job, requires a form of problem-solving that’s not really taught in math or economics classes: educated guessing. They’re also the kind of questions at the center of a new book by Sanjoy Mahajan, a physicist and associate director of M.I.T.’s Teaching and Learning Laboratory.

Street-Fighting Mathematics espouses a different kind of problem-solving than many people are accustomed to, one that’s attuned to real-world problems and requires less rigor than usual (as Mahajan puts it: “rigor leads to rigor mortis”). In a recent interview with The Chronicle of Higher Education, Mahajan estimated the amount of money in a Brinks truck and the annual state budget of Delaware.

Mahajan has agreed to field questions from Freakonomics readers, so let them fly in the comments section below and, as always, we’ll post his answers in short course.


what is the probability that a lung full of air breathed in today in New York contains at least one moleule of air that Christ exhaled with his last breath on the cross?

(this was a question in a Cambridge University Physics Entrance Paper)


Years until we discover extraterrestrial intelligent life, and/or probability that extraterrestrial intelligent life exists


I know this makes me a philistine, but of what value is pi over, say, establishing that pi is EXACTLY 3.14?

That is, what would be lost or gained if instead of an endless number, we established that pi is this much and no more or less? Would our circles be clearly distorted? Would some mathematical principles tumble?

I'm not trying to be difficult. I simply want to know.

Bobby G

How does one improve his ability to make educated guesses? Is it just something one is born with?


What's the rate of flow of oil from the Deep Horizon oil rig and what will the total amount of oil spilled be?


How much change do I have in my pocket?

Sharon LaFleur

How long will it take the oil in the gulf to become fish food and what will be the increased (or not) number of fish because of this influx of new food?


How many licks does it take to get to the center of a Tootsie Roll Tootsie Pop?

Drill-Baby-Drill Drill Team

There is only ONE RULE in Street Fighting Mathematics:

1. There are No Rules.

2. Don't talk about the Math Club.


How many barrels of crude are leaking into the Gulf of Mexico every day?


How many feathers on a purdue chicken?


How many spiders are in an average urban 12-storey building?


What is the air-speed velocity of an unladen swallow?


How much wood would a woodchuck chuck if a woodchuck could chuck wood?


How many atheists are vegetarians and how many vegetarians are atheists?


How long ago was the energy in my Big Mac sunlight?

Mr. K

> How does one improve his ability to make educated guesses?

This is what I've been struggling with as a math educator for several years.

Turns out, the easy answer is "Just Do It". The hard part is coming up with questions that motivate youre students.


what about the problem of bias in 'street math'?- seems to me that rigor is the safeguard against bias hijacking estimates for manipulative ends- i remember during the presidential campaign that estimates of palin rally attendance became controversial along these lines of street estimates- and also, much more troubling, is the 'guestimation' that went on in the financial industry, where the banks colluded with ratings agency guestimates on securities which were rigged to overinflate prices, thereby exploiting investor bias during a boom time (becoming blinded to the downside)


The recent economy has created a situation in which newly minted graduates are having difficulty getting jobs. One would expect that the situation would also have an effect on the creation of families, i.e. getting married, having kids, etc.

So two questions: First, is there going to be an effect on the American family that keeps young adults in the house longer due to delay of starting their own households.

Second, Which type of housing will enoy the most growth in the next 5, 10, or 20 years. Apartments, single family houses, condos, or some other form of housing.

Delving into past recessions and depressions I don't think will help with this question, because none of those other eras had the breadth of communication that the present enjoys.


If a butterfly flaps its wings in China, how long would it take for me (in Washington DC) to feel the resulting hurricane (or butterfly-wingflap-sized gust of wind)?