The most awkwardly named function in MATLAB


(via Reddit)

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Online Math Class…Fail…indeed


Online Math Class...Fail



Thanks to Kei for this submission! And sorry you got the answer not correct… :-)
He says:

I did click “No” lol ( That is why there is no red “x” ) Sorry…but still nice work ahahh”

*If you have something funny related to math, then submit it to MathFail using our submission page and it might be posted. Cheers!

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Another crackpot “mathematician”

There’s lots of crackpots on the internet (and off the internet) who don’t understand some of the basics in mathematics. This person claims that:

“In 4,000 years of mathematics no one has been able to show a ratio for pi. We will show just how to produce that ratio. They state that pi is the ratio of the circumference of a circle to its diameter and then go on to prove that there is no ratio. Therefore concluding that the ratio is only a mere approximation of a true value. You will be surprised about how to establish a ratio for pi as well as how to prove that the present day calculation for pi is invalid.”

They later go on to prove that pi = 201 / 64 by using “addition – subtraction – multiplication – division and square root extraction”.

Located at PureMathTheory.com.

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Bike with square wheels

I’m back to my regular update schedule. I was just visiting Macalester College and saw that they had the tricycle pictured below! I have seen pics on the internet of it but didn’t know where it existed.


bike

The original was created in 1997 (and replaced in 2004) by Professor Wagon (not Professor Bike) and rolls smoothly over a road made out of inverted “catenaries”. See a video here for a demonstration.

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Making change


dollar-sign
dollar-sign
dollar-sign
dollar-sign
dollar-sign
dollar-sign
dollar-sign

Consider the following hypothetical situation:

You are a cashier and you have to give the customer $0.40 in change, however, you have no nickels left in your till. The goal is to minimize the number of coins that the customer receives. How do you do it?

Well this actually happened, and the process the cashier went through was to:

  • first take out a quarter (the highest denomination coin below $0.40),
  • then take out a dime (the next highest denomination below $0.15),
  • then finally, take out 5 pennies (since there is no nickels).

This produces 7 coins! The cashier realized this was not good, thought for a moment, then grabbed 4 dimes, which is the optimal solution in this case.

The “Change-making problem” is a well known problem you may have encountered if you have studied optimization. The problem is to see how one can give change with the least number of coins of given denominations.

The interesting thing is that for currency in North America, the greedy algorithm always produces an optimal solution (i.e. picking the largest denomination of coin which is not greater than the remaining amount). As we saw in the above example, if nickels were not allowable coins, the greedy algorithm would no longer produce an optimal solution for our currency denominations.

Check out the wikipedia links above for more info about this problem :P

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Caution!

This is in a textbook:


calculus caution


CAUTION!
The area of a washer is pi*R^2-pi*r^2, which you can simplify to pi*(R^2-r^2), but not to pi*(R-r)^2. No matter how tempting it is to make the latter simplification, it’s wrong. Don’t do it.

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Free time graph


free time graph

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The average person has one testicle and one ovary…

The first one is how to cheer up your friend…


spiked math one testicle comic




Just don’t tell him he should have one ovary :P

statistics show one testicle and one ovary


This actually appeared in a textbook…

yahoo answers fail

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Addition Fail

addition-fail.jpg

Link: http://www.youtube.com/watch?v=VTNXlHY7YSk
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Deck Shuffling


shuffling a deck of cards

Cool fact: If you thoroughly shuffle an ordinary deck of 52 playing cards, chances are that the resulting arrangement of cards has never existed before (via Reddit and Reddit).

Quoting from the math subreddit:

Proof — easy numeric comparison. There are 52! possible orderings of a deck, and I’m assuming all are equally likely after your shuffling. Let’s wildly overestimate and assume that every second since the universe was created, a million decks of cards were shuffled and someone looked through them. Thus fewer than 10^24 orderings have ever been seen.

But at an incredibly crude estimate, 52! is at least 10^42 * 10!; let’s underestimate that again wildly by 10^42. That means that chances of your ordering ever having come up previously are at most 1 in 10^18.

(Note, by the birthday paradox, the chances that there have been two identical orderings observed by two people in history are quite a bit higher — perhaps even feasibly likely; I haven’t calculated it. But we’re looking here at the probability that a given ordering matches one of the ones previously seen.)

Discussion here.

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