No Bull — This is My New Favorite Fermi Question

November 6, 2018 at 10:29 pm 4 comments

It’s hard to say which emotion was strongest — awe, bewilderment, admiration, horror, fear — when I heard the following statistic:

McDonald’s sells 75 hamburgers every second.

McDonald's Logo

But I’m a math guy, so there’s no doubt where my mind turned after that emotion passed:

How many cows is that?

Have at it, internet.

What do you get when you divide the circumference of a bovine by its diameter?
Cow pi.

What is the favorite course at Bovine College?

A mathematician counted 196 cows in the field. But when he rounded them up, he got 200.


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Math Words for National Dictionary Day What’s in Your Pocket?

4 Comments Add your own

  • 1. Xander  |  November 7, 2018 at 12:26 am

    What a fun and silly Fermi approximation!

    Here’s my try: a burger is about 1/10 pound of cow and Micky-Dees serves about 100 burgers per second, so 10 lbs of ground cow per second. A cow is about 1000 lbs, but lots of that is bone, gristle, better cuts of meat that aren’t burger-ified, and so on. Let’s say that 10% of a cow is ground beef-able, so 1 cow gives about 100 lbs of burger.

    At 10 lbs per second, and 100 lbs per cow, it looks like McDonalds serves about 1 cow every 10 seconds.

    • 2. venneblock  |  November 7, 2018 at 8:02 am

      Hmm. McDonald’s brags that their “big” patties are quarter-pounders, which is 1/4 pound. I don’t know the exact size of their smaller patties (the ones they use on a regular hamburger), but I suspect it’s more than 1/10 pound. And I do have first-hand knowledge — I worked at McDonald’s for about 6 months in high school. Though happily, I usually worked the early shift, so I got to spend 5/8 of my shift making pancakes and eggs, which was way less greasy than flipping burgers.

      But finishing your logic, X, that’s 6 cows a minute, 360 cows an hour, or about 8,640 cows a day.

      • 3. Xander  |  November 7, 2018 at 3:17 pm

        My understanding of Fermi approximation is that the goal is to do everything in powers of 10, as that makes things a *lot* easier. If a “big” patty is a quarter of a pound, then a “typical” patty is likely smaller. Given the choice between an estimate of 1/10 of a lb or 1 lb, the smaller quantity seems more apt.

        By the way, I spent some time Googling this yesterday. I can’t find any good answer to the question of “How many burgers do you get out of a cow?”, but unreliable sources on the interwebs seem to give a number around 100 lbs of ground beef per cow (with more ground beef coming from cull cows… ewww…). McDonalds claims to use 190,000 lbs of ground beef per day (or did in 2013, anyway), which is something on the order of 1900 cows per day. So, the two estimates don’t disagree by *too* much (order-of-magnitude speaking).

      • 4. venneblock  |  November 7, 2018 at 8:59 pm

        Huh. I’ve never heard the powers-of-10 thing for Fermi approximations, but makes sense.

        Today I Found Out estimates 450 burgers per cow… but that would violate your powers-of-10 rule:

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The Math Jokes 4 Mathy Folks blog is an online extension to the book Math Jokes 4 Mathy Folks. The blog contains jokes submitted by readers, new jokes discovered by the author, details about speaking appearances and workshops, and other random bits of information that might be interesting to the strange folks who like math jokes.

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