Archive for November, 2017

Fowl Formulae for Thanksgiving

Okay, I know you’re going to find this hard to believe, but there is disagreement on the internet. And I don’t mean about some insignificant topic like gun control or taxes or health care or the value of 6 ÷ 2(1 + 2). This is big. This is important.

We’re talking turkey. Literally.

According to the British Turkey Information Service — yes, there really is such an agency — the amount of time you should cook your turkey at 375° F can be found with the following formula:

t =    \begin{cases}    20w + 70 & w < 4; \\    20w + 90 & w \geq 4,    \end{cases}

where t is the cooking time in minutes and w is the weight of the turkey in kilograms.

If you’d rather not do the math yourself, try the British Turkey Cooking Calculator, which will not only give you the cooking time but also the defrosting time and the size of turkey to buy for a given number of servings.

By comparison, the Meat Chart provided by FoodSafety.org says that turkey should be cooked at 325° F for 30 minutes per pound.

But the cooking website allrecipes.com says that only 20 minutes per pound is sufficient if you bake the bird at 350° F.

Whereas the good folks at delish offer the following guidelines:

Delish - Turkey Cooking Times

Cooking Times at 325° F from delish.com

which translates to the lovely formula

t =    \begin{cases}    5w + 125 & w \leq 10; \\    15w & w = 12; \\    7.5w + 120 & w \geq 14,    \end{cases}

but requires that you interpolate if your bird weighs an odd number of pounds. (Like 86 pounds, the world record for heaviest turkey ever raised. Even though the units digit is 6, you’d agree that 86 is an odd number of pounds for the weight of a turkey, no?)

As you might suspect, Wolfram Alpha has a more mathematically sophisticated formula:

\displaystyle t = T \times \left( \frac{w}{20} \right)^\frac{2}{3}

where t is the cooking time in hours, w is the weight in pounds, and T is a coefficient to account for cooking environment. For normal conditions, T = 4.5, and the equation reduces to

\displaystyle t = 36.64w^\frac{2}{3}

if you use minutes instead of hours for the unit of time.

But this feels a little like a math joke; below the formula, Wolfram offers the following:

using the heat equation for a spherical turkey in a 325° F oven

Falling into the wrong hands, that idea could lead to an horrendous modification of the spherical cow joke…

The turkeys at a farm were not gaining sufficient weight in the weeks leading up to Thanksgiving, so the farmer approached a local university to ask for help. A theoretical physicist was intrigued by the problem and offered his assistance. He spent several weeks at the farm, examining the turkeys and filling his notebook with equation after equation. Finally, he approached the farmer and said, “I have found a solution.”

“Oh, that’s excellent!” said the farmer.

“Yes,” said the physicist. “Unfortunately, it only works for spherical turkeys in a vacuum.”

The Wolfram formula is very similar to one suggested by physicist Pief Palofsky, who apparently dabbled in poultry when not winning the National Medal of Science.

\displaystyle t = \frac{2}{3} w^\frac{2}{3}

and when converted to minutes instead of hours, this becomes

\displaystyle t = 40w^\frac{2}{3}.

According to Turkey for the Holidays, the average weight of a turkey purchased at Thanksgiving is 15 pounds. The cooking times for a 15-pound bird, based on the formulae above, appear to have been chosen by a random number generator.

Recommender Time (min) Temp (° F)
British Turkey Information Service 226 minutes 375
Foodsafety.org 450 minutes 325
allrecipes.com 300 minutes 350
delish.com 233 minutes 325
Wolfram Alpha 223 minutes 325
Pief Palofsky 243 minutes 325

Even if you limit consideration to those who suggest a cooking temp of 325° F, the range of times still varies from just under 2¾ hours to a staggering 7½ hours. Wow.

With Thanksgiving just around the corner, where does all of this contradictory information leave us?

A number of sites on the internet claim that the only way to adequately check the doneness of a turkey is with a meat thermometer.

turkeyThe folks at recipetips.com claim that a turkey can be removed when the temperature is at least 170° F for the breast and 180° F for the thigh. Yet on the very same page, they claim, “Turkey must reach an internal temperature of 185° F.”

On the other hand, the folks at the Food Lab claim a turkey can be safely removed when the breast temperature reaches 150° F, because after resting 15‑20 minutes before carving, the amount of remaining bacteria will be minimal. They explain, “What the USDA is really looking for is a 7.0 log10 relative reduction in bacteria,” particularly Salmonella, which means that only 1 out of every 10,000,000 bacteria that were on the turkey to start with will survive the cooking process. And according to the USDA guidelines, a turkey that maintains a temperature above 150° F for 3.8 minutes or longer will reach that threshold for safety.

Which has to make you wonder — if 3.8 minutes at 150° F is supposedly adequate, why then does the USDA Food Safety and Inspection Service recommend that the minimum internal temperature of the turkey in the thigh, wing, and breast should be at least 165° F? Who knows. I suspect it’s typical government over-engineering to remove all doubt.

So, how long should you cook your turkey? Hard to say. But if you put your turkey in the oven right now, it should be done by November 23.

When the turkey is finally ready, here are a few math jokes you can tell around the Thanksgiving table.

What do math teachers do on Thanksgiving?
Count their blessings!

What does a math teacher serve for dessert on Thanksgiving?
Pumpkin Pi.

How do you keep private messages secure on Thanksgiving?
Public turkey cryptography.

Thanksgiving dinners take 18 hours to prepare. They are consumed in 12 minutes. Halftimes take 12 minutes. This is not coincidence. 
~ Erma Bombeck

Gobble, gobble!

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November 14, 2017 at 12:32 pm Leave a comment

The Virginia Governor’s Race and MP.6

Hotly contested. Particularly nasty. Ugly. Uncivilized. Controversial. Disgusting. Dirty.

Those are just some of the words and phrases used to describe this year’s race for governor in my home state of Virginia. It’s part of the reason that we had the highest voter turnout for a gubernatorial election in 20 years. It’s also why every citizen in the Old Dominion was anxiously awaiting the results.

I was no different. At 8:30 p.m. EST, I strolled on over to POLITICO, where I was presented with more information that I could handle:

VA Election Results - 8:31 p.m.

VA Gubernatorial Results at 8:31 p.m. EST

It was surprising that Northam had a 5.8% lead, since some recent polls suggested that his lead had dwindled to as little as 3.3%. It was surprising that only 90 minutes after the polls had closed, many news organizations were already declaring Northam the winner. But it was outright astonishing that POLITICO was displaying the percent of precints reporting as:

72.68121590023384%

WTF?

On Feburary 13, 2011, in a post titled Statistically Speaking…, I presented the following joke:

69.8724% of all statistics reflect an unjustified level of precision.

Three years later, in a post titled Sound Smart with Math Words, I presented another version of that same joke, though this time the percentage was expressed to the millionths:

An unprecedented 69.846743% of all statistics reflect an unjustified level of precision.

Did I think the additional precision would make it more obvious that the sentence was actually a joke? Or did I just think it would make it funnier? I’m not sure.

But I do know that it would never have occurred to me to take the level of precision to 14 — count them, 14! — digits of accuracy beyond the decimal point.

But POLITICO thought it was necessary.

That’s right. They calculated and displayed the percent of precincts reporting to the hundred-trillionths place. Hundred. Trillionths.

That’s like stating the winning time for the Tour de France to the nearest millisecond.

Or estimating the weight of the Earth to the nearest gram.

In fairness to POLITICO, though, the percentages that they were reporting not only reflected an unjustified level of precision. They were also wrong.

According to the Virginia Department of Elections, there are 2,567 precincts in the commonwealth. If 1,865 precincts had submitted results, the percent of precincts reporting could have been displayed as:

72.6529%

If 1,866 precincts had turned in their results, the percent of precincts reporting could have been displayed as:

72.6918%

But there is no number of precincts for which the percent could have been reported as:

72.68121590023384%

So, either POLITICO was using an incorrect denominator, or their algorithm was incorrectly calculating percentages.

Oh, well. At least they got the election results correct. (I hope.)

In their defense, they did finally make a correction. When I checked the results at 9:24 p.m. EST, this is what was presented:

Virginia Election Results - 9:24 p.m.

VA Gubernatorial Results at 9:24 p.m. EST

The percentage of precincts was displayed as a more reasonable 97.74%. From this, I can surmise that 2,509 precincts had reported their results (since 2,509 / 2,567 = 0.9774) and that POLITICO had finally found someone who was nimble with a slide rule.

November 8, 2017 at 5:51 am Leave a comment

Interactions with Fractions

This math factoid, compliments of Learn Fun Facts, is just too good not to share…

\displaystyle \frac{18\,534}{9\,267} \times \frac{17\,469}{5\,823} = \frac{34\,182}{5\,697}

Ah, but maybe you missed it. Did you notice that each digit 1-9 appears exactly once in all three fractions? Pretty cool. But I have to say that this is still my favorite fraction equation:

\displaystyle \frac{1}{2} + \frac{1}{3} + \frac{1}{6} = 1

Simple. Beautiful.

On the other hand, I’m not sure I have a favorite fraction joke. I mean, how do you pick just one? The number of fraction jokes is a lot like

\displaystyle \lim_{x\to 0} \frac{1}{x}.

That’s right. There’s no limit.

5 out of 4 people have trouble with fractions.

I will express polynomials as partial fractions. I will compute the value of continued fractions. I will even find a least common denominator. But I draw the line between the numerator and denominator.

What is one-fifth of a foot?
A toe.

How many tents can fit in a campground?
Ten, because ten tents (tenths) make a whole!

Before you go, here’s a fun little fraction problem for you:

What is 1/2 of 2/3 of 3/4 of 4/5 of 500?

November 3, 2017 at 6:58 am Leave a comment


About MJ4MF

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.

MJ4MF (offline version)

Math Jokes 4 Mathy Folks is available from Amazon, Borders, Barnes & Noble, NCTM, Robert D. Reed Publishers, and other purveyors of exceptional literature.

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