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Apple season is upon us, and with it, a certain autumnal mix of glee and anxiety over which variety of apples to stock up on this season.

Stress no longer: Slate asked Andrew Mikolajski—author of The Illustrated World Encyclopedia of Apples—for his thoughts and compiled them into a fun and incredibly informative chart.

From Granny Smith to Jonagold to Esopus Spitzenburg (which is apparently an apple variety and Thomas Jefferson’s favorite), this fruity flowchart will ensure you don’t juice a Baldwin apple when you should be throwing it at a wall.

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5 Ways You Do Complex Math in Your Head Without Realizing It
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The one thing that people who love math and people who hate math tend to agree on is this: You're only really doing math if you sit down and write formal equations. This idea is so widely embraced that to suggest otherwise is "to start a fight," says Maria Droujkova, math educator and founder of Natural Math, a site for kids and parents who want to incorporate math into their daily lives. Mathematicians cherish their formal proofs, considering them the best expression of their profession, while the anti-math don't believe that much of the math they studied in school applies to "real life."

But in reality, "we do an awful lot of things in our daily lives that are profoundly mathematical, but that may not look that way on the surface," Christopher Danielson, a Minnesota-based math educator and author of a number of books, including Common Core Math for Parents for Dummies, tells Mental Floss. Our mathematical thinking includes not just algebra or geometry, but trigonometry, calculus, probability, statistics, and any of the at least 60 types [PDF] of math out there. Here are five examples.

#### 1. COOKING // ALGEBRA

Of all the maths, algebra seems to draw the most ire, with some people even writing entire books on why college students shouldn't have to endure it because, they claim, it holds the students back from graduating. But if you cook, you're likely doing algebra. When preparing a meal, you often have to think proportionally, and "reasoning with proportions is one of the cornerstones of algebraic thinking," Droujkova tells Mental Floss.

You're also thinking algebraically whenever you're adjusting a recipe, whether for a larger crowd or because you have to substitute or reduce ingredients. Say, for example, you want to make pancakes, but you only have two eggs left and the recipe calls for three. How much flour should you use when the original recipe calls for one cup? Since one cup is 8 ounces, you can figure this out using the following algebra equation: n/8 : 2/3.

Lucy Quintanilla

However, when thinking proportionally, you can just reason that since you have one-third less eggs, you should just use one-third less flour.

You're also doing that proportional thinking when you consider the cooking times of the various courses of your meal and plan accordingly so all the elements of your dinner are ready at the same time. For example, it will usually take three times as long to cook rice as it will a flattened chicken breast, so starting the rice first makes sense.

"People do mathematics in their own way," Droujkova says, "even if they cannot do it in a very formalized way."

#### 2. LISTENING TO MUSIC // PATTERN THEORY AND SYMMETRY

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The making of music involves many different types of math, from algebra and geometry to group theory and pattern theory and beyond, and a number of mathematicians (including Pythagoras and Galileo) and musicians have connected the two disciplines (Stravinsky claimed that music is "something like mathematical thinking").

But simply listening to music can make you think mathematically too. When you recognize a piece of music, you are identifying a pattern of sound. Patterns are a fundamental part of math; the branch known as pattern theory is applied to everything from statistics to machine learning.

Danielson, who teaches kids about patterns in his math classes, says figuring out the structure of a pattern is vital for understanding math at higher levels, so music is a great gateway: "If you're thinking about how two songs have similar beats, or time signatures, or you're creating harmonies, you're working on the structure of a pattern and doing some really important mathematical thinking along the way."

So maybe you weren't doing math on paper if you were debating with your friends about whether Tom Petty was right to sue Sam Smith in 2015 over "Stay With Me" sounding a lot like "I Won't Back Down," but you were still thinking mathematically when you compared the songs. And that earworm you can't get out of your head? It follows a pattern: intro, verse, chorus, bridge, end.

When you recognize these kinds of patterns, you're also recognizing symmetry (which in a pop song tends to involve the chorus and the hook, because both repeat). Symmetry [PDF] is the focus of group theory, but it's also key to geometry, algebra, and many other maths.

#### 3. KNITTING AND CROCHETING // GEOMETRIC THINKING

Cheryl, Flickr // CC BY-SA 2.0

Droujkova, an avid crocheter, she says she is often intrigued by the very mathematical discussions fellow crafters have online about the best patterns for their projects, even if they will often insist they are awful at math or uninterested in it. And yet, such crafts cannot be done without geometric thinking: When you knit or crochet a hat, you're creating a half sphere, which follows a geometric formula.

Droujkova isn't the only math lover who has made the connection between geometry and crocheting. Cornell mathematician Daina Taimina found crocheting to be the perfect way to illustrate the geometry of a hyperbolic plane, or a surface that has a constant negative curvature, like a lettuce leaf. Hyperbolic geometry is also used in navigation apps, and explains why flat maps distort the size of landforms, making Greenland, for example, look far larger on most maps than it actually is.

#### 4. PLAYING POOL // TRIGONOMETRY

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If you play billiards, pool, or snooker, it's very likely that you are using trigonometric reasoning. Sinking a ball into a pocket by using another ball involves understanding not just how to measure angles by sight but triangulation, which is the cornerstone of trigonometry. (Triangulation is a surprisingly accurate way to measure distance. Long before powered flight was possible, surveyors used triangulation to measure the heights of mountains from their bases and were off by only a matter of feet.)

In a 2010 paper [PDF], Louisiana mathematician Rick Mabry studied the trigonometry (and basic calculus) of pool, focusing on the straight-in shot. In a bar in Shreveport, Louisiana, he scribbled equations on napkins for each shot, and he calculated the most difficult straight-in shot of all. Most experienced pool players would say it’s one where the target ball is halfway between the pocket and the cue ball. But that, according to Mabry’s equations, turned out not to be true. The hardest shot of all had a surprising feature: The distance from the cue ball to the pocket was exactly 1.618 times the distance from the target ball to the pocket. That number is the golden ratio, which is found everywhere in nature—and, apparently, on pool tables.

Do you need to consider the golden ratio when deciding where to place the cue ball? Nope, unless you want to prove a point, or set someone else up to lose. You're doing the trig automatically. The pool sharks at the bar must have known this, because someone threw away Mabry's math napkins.

#### 5. RE-TILING THE BATHROOM // CALCULUS

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Many students don't get to calculus in high school, or even in college, but a cornerstone of that branch of math is optimization—or figuring out how to get the most precise use of a space or chunk of time.

Consider a home improvement project where you're confronted with tiling around something whose shape doesn't fit a geometric formula like a circle or rectangle, such as the asymmetric base of a toilet or freestanding sink. This is where the fundamental theorem of calculus—which can be used to calculate the precise area of an irregular object—comes in handy. When thinking about how those tiles will best fit around the curve of that sink or toilet, and how much of each tile needs to be cut off or added, you're employing the kind of reasoning done in a Riemann sum.

Riemann sums (named after a 19th-century German mathematician) are crucial to explaining integration in calculus, as tangible introductions to the more precise fundamental theorem. A graph of a Riemann sum shows how the area of a curve can be found by building rectangles along the x, or horizontal axis, first up to the curve, and then over it, and then averaging the distance between the over- and underlap to get a more precise measurement.

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The Sky Was No Limit: The WASP Women Pilots of WWII
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Shirley Slade sat on the wing of a plane and looked off into an uncertain future. Slade—clad in her flight suit with pigtails guarding against Texas wind—was posing for the July 19, 1943 issue of Life magazine, and the composition between the aircraft and its operator was a juxtaposition spelled out in the cover headline: "Air Force Pilot."

Slade was one of more than 1000 women who had been solicited by the U.S. government to enter an intensive seven-month training course that would make them the first female pilots to enter the Air Force. What had been a boy's club was being forced into a kind of reluctant gender neutrality as a result of World War II and severe pilot shortages. By recruiting women, the Air Force could maintain delivery of aircraft, ferry supplies, and perform other non-combative functions that fueled the war efforts. Collectively, the group would become known as WASPs: Women Airforce Service Pilots.

While all of these women risked their lives—and more than a few lost them—they were not perceived as equals. Because they were designated as civilians, they were denied military honors and compensation. As the war wound down, men returning from combat jockeyed to take the WASPs' places as active-duty pilots. Occasionally, the women would be used in target practice. It would be decades before the women of WASP would finally get their due.

America's entry into World War II following the attack on Pearl Harbor heralded a new policy of rationing. Food, materials, and manpower were doled out carefully, but demand for pilots quickly exceeded the available personnel. By 1942, the Air Force realized they would have to tap into new sources in order to continue their campaign.

Jacqueline Cochran had a solution: A pilot in her own right and a contemporary of Amelia Earhart, Cochran knew there was a strong contingent of female fliers who had licenses and had logged air time who could be recruited for support missions. She petitioned the Air Force, including commanding general Henry Harley "Hap" Arnold, to approve a training program that would ultimately relocate volunteers to Avenger Field in Sweetwater, Texas. Another pilot, Nancy Harkness Love, submitted a similar proposal.

WASP pilot Elizabeth Remba Gardner
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Cochran and Love were up against considerable resistance to involving women in military efforts. General Dwight D. Eisenhower once admitted he was "violently against" the idea (before concluding that none of his concerns came to light and women were an integral part of the effort). Internally, there was concern as to whether women would even be capable of handling a massive aircraft like the B-29 bomber, so superiors hedged their bets by creating two organizations.

Love was put in charge of the Women's Auxiliary Ferrying Squadron (WAFS)—an organization to ferry planes—while Cochran was put in charge of the Women's Flying Training Detachment, which did whatever the Army Air Corps required of it. A little under a year later, these two groups were merged into a single organization: the WASPs. This new group demanded that incoming women logged at least 35 hours of flight time before coming to Sweetwater. More importantly, the women would be considered civilians, not military personnel.

Roughly 25,000 women applied; around 1900 were accepted and 1100 completed training. On their own dimes, these women streamed into Texas to begin the seven-month program that taught them every aspect of military flying except for gunnery duty and formation flying. Every day in the barracks included intensive lessons, physical fitness training, and studying. At night, the women would dance, sing, or play ping-pong. Life described their ambitions as "piloting with an unfeminine purpose" and noted that some of the women needed cushions in order to sit comfortably in planes designed for male bodies. Their mascot, a tiny winged sprite named Miss Fifinella, was designed by Disney, and the patch appeared on many of their jumpsuits and plane noses.

According to Life, the Air Force reported that the women were faster on instruments while the men "had better memory for details." But in virtually every way that counted, the magazine wrote, there was no practical difference in ability.

Graduates were dispatched to bases around the country, though the most pressing job was ferrying new aircraft from factories to places like Newark, New Jersey, where the planes would make the jump overseas. The women shuttled 12,000 of these planes during the war. They also escorted military chaplains from base to base on Sundays for religious services and operated test flights for repaired aircraft to make sure they were safe to fly in combat. Sometimes, they'd be tasked with towing targets behind them so soldiers could use live ammunition for combat practice.

Simulated combat may have been nerve-wracking, but it was no more dangerous than the actual flying and the very real possibility that the WASPs would experience equipment malfunction or fuel issues. In the two years the squad was active, 38 women perished during missions. At the time—and for decades afterward—the families of those women were denied many of the basic privileges afforded to the families of their male counterparts. When a WASP died, her colleagues—not the government—would pitch in to pay for her burial. Their families were prohibited from putting a gold star in their windows, a sign of a military casualty, nor were they "allowed" to drape the American flag over their coffins.

On December 20, 1944, the WASPs were sent home. The war wasn't yet over, but men returning from the front lines were dismayed that jobs they expected to find waiting for them were being occupied by women. Despite Cochran's petition to have the WASPs permanently incorporated into the Air Force, Congress turned her down.

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The pride the women had felt serving their country turned to confusion. By being classified as "civilians," the WASPs found little respect for their efforts. When entering the workforce after the war, some even became flight attendants, as no commercial airline would hire a female pilot.

In the 1970s, the Air Force announced they'd be accepting female recruits for the "first time," a proclamation that angered the surviving WASPs. Their efforts had largely gone unheralded, and now it seemed like the government was wiping them from history completely. Petitioning for recognition and receiving aid from fellow war ferry pilot Senator Barry Goldwater, they were finally granted military status on November 23, 1977.

As the WASPs aged, a handful got the chance to enjoy another honor. In 2010, the women were awarded the Congressional Gold Medal for their efforts. After flying 77 different types of planes over 60 million miles during wartime and being largely ignored for decades, it was recognition that was long overdue.

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