Danica McKellar Interview

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I recently watched a remarkable and surprising interview on Numberphile of the actress Danica McKellar.  She began as a child actress and recently has played romantic roles on the Hallmark series of TV movies.  So it comes as a surprise to find she was an undergraduate math major, and with a female colleague and the help of their advisor one summer proved a theorem involving math and metallurgy.

She was terrifically articulate and enthusiastic during the interview and made a number of telling observations that would be helpful for any student, especially girls, who might find they like math in grade school and might even consider majoring in it in college.

Her big emphasis was on self-esteem and the importance of reaching girls to support any interest they might have in math against the negative forces they often experience.  To this end she has written a series of math books, each tailored to a different grade-level of students.  But she feels the middle school years are especially critical to support girls in math.

Perhaps the thing I liked best in the interview (maybe because it echoed my own views) was her attitude towards math—she loved solving puzzles.  In fact, just doing math was its own reward.  She politely deflected all efforts by Brady, the interviewer, to ask if she regretted not pursuing a professional career more devoted to math.  Not to knock Brady’s fine interview but I found this line of questioning supporting the current utilitarian view of education (What good is it, how can it be of use to help me earn a living) to be a bit condescending.  And there was even a whiff of what the most important thing to do with math and what the professors are training students for is math research.   Since most math majors and even math Ph.D.s are not going to find employment in academia, math as an ancillary component to one’s career is the most one could imagine in this context.  But above and beyond that is the real truth: math is fun for its own sake, and Danica McKellar championed that in spades.  I don’t think I have seen anyone unabashedly extol the joys of doing math as well as she did.

I heartily recommend this interview to anyone, especially young girls, who might have a secret affection for mathematics but fear some stigma that might attach to them if they admitted it.

Some links from Youtube:

For a PDF version see Danica McKellar Interview.

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Horses to Qi

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This is a challenging problem from the c.100AD Chinese mathematical work, Jiǔ zhāng suàn shù (The Nine Chapters on the Mathematical Art) found at the MAA Convergence website.

“Now a good horse and an inferior horse set out from Chang’an to Qi.  Qi is 3000 li from Chang’an.  The good horse travels 193 li on the first day and daily increases by 13 li; the inferior horse travels 97 li on the first day and daily decreases by ½ li.  The good horse reaches Qi first and turns back to meet the inferior horse.  Tell: how many days until they meet and how far has each traveled?”

The solution involves common fractions, which the Chinese were already adept at using by 100 BC.

Answer.

See Horses to Qi for a solution.

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Making Arrows

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This is an interesting problem from 180 BC China.

“In one day, a person can make 30 arrows or fletch [put the feathers on] 20 arrows.  How many arrows can this person both make and fletch in a day?”

It turns out the solution to this problem led me into the history of numerator/denominator (aka common) fractions, a subject I had been finding difficult to track down.

Answer.

See Making Arrows for a solution.

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Hjelmslev’s Theorem

I came across this remarkable result in Futility Closet:

“On each of these two black lines is a trio of red points marked by the same distances.  The midpoints of segments drawn between corresponding points are collinear.

(Discovered by Danish mathematician Johannes Hjelmslev.)”

This result seems amazing and mysterious.  I wondered if I could think of a proof.  I found a simple approach that did not use plane geometry.  And suddenly, like a magic trick exposed, the result seemed obvious.

See Hjelmslev’s Theorem

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Classic Geometry Paradox

Coming across this classic geometric paradox recently in Futility Closet motivated me to write down its solution in detail.

“Where did the empty square come from?”

In any case, this is the canonical example for why I avoid visual geometric proofs—you can be so easily fooled.  Real proofs require plane or analytic geometry arguments.

See the Classic Geometry Paradox

 

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Box Code Puzzle

This is an intriguing puzzle from Futility Closet.

“In Robert Chambers’ 1906 novel The Tracer of Lost Persons, Mr. Keen copies the figure below from a mysterious photograph. He is trying to help Captain Harren find a young woman with whom he has become obsessed.

‘It’s the strangest cipher I ever encountered,’ he says at length. ‘The strangest I ever heard of. I have seen hundreds of ciphers—hundreds—secret codes of the State Department, secret military codes, elaborate Oriental ciphers, symbols used in commercial transactions, symbols used by criminals and every species of malefactor. And every one of them can be solved with time and patience and a little knowledge of the subject. But this … this is too simple.’

The message reveals the name of the young woman whom Captain Harren has been seeking. What is it?”

As is usual with these types of puzzles, I felt foolish that I couldn’t see the immediate, simple interpretation of the boxes—after a great deal of effort.  So I solved it using the usual cryptographic methods that rely heavily on logic and letter frequencies, though the message is a bit short for that.

Answer.

See Box Code Puzzle for solutions.

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Learning Mathematics

In one of our periodic FaceTime calls I found out that my granddaughter in 6th grade was interested in learning algebra and had gotten a book to help her out.  Clearly this initiative to get a head start prior to the normal course curriculum excited me, so I wrote what I thought was an insightful essay on the meaning and purpose of algebra.  Needless to say it was an abysmal failure.

That got me to thinking deeply about what it meant to learn mathematics and in particular symbolic algebra.

See Learning Mathematics

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Weight of Potatoes

The following is another puzzle from the Irishman Owen O’Shea.

“Suppose you buy 100 pounds of potatoes and you are told that 99 percent of the potatoes consist of water.

You bring the potatoes home and leave them outside to dehydrate until the amount of water in the potates is 98 percent.  What is the weight of the potatoes now?”

This problem takes a little concentration to get right and the solution is a bit surprising at first.

Answer

See Weight of Potatoes for solutions.

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Locating the Loot

This is a straight-forward problem from Geoffrey Mott-Smith in 1954.

“A brown Terraplane car whizzed past the State Police booth, going 80 miles per hour. The trooper on duty phoned an alert to other stations on the road, then set out on his motorcycle in pursuit. He had gone only a short distance when the brown Terraplane hurtled past him, go­ing in the opposite direction. The car was later caught by a road block, and its occupants proved to be a gang of thieves who had just robbed a jewelry store.

Witnesses testified that the thieves had put their plunder in the car when they fled the scene of the crime. But it was no longer in the car when it was caught. Reports on the wild ride showed that the only time the car could have stopped was in doubling back past the State Police booth.

The trooper reported that the point at which the car passed him on its return was just 2 miles from his booth, and that it reached him just 7 minutes after it had first passed his booth. On both occasions it was apparently making its top speed of 80 miles per hour.

The investigators assumed that the car had made a stop and turned around while some members of the gang cached the loot by the roadside, or perhaps at the office of a “fence.” In an effort to locate the cache, they assumed that the car had maintained a uniform speed, and allowed 2 minutes as the probable loss of time in bringing the car to a halt, turning it, and regaining full speed.

On this assumption, what was the farthest point from the booth that would have to be covered by the search for the loot?”

Answer.

See Locating the Loot for solutions.

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