Science & TechnologyDEC 18, 2023

30 'Useless Yet Interesting Calculations' To Get Your Mind Reeling (New Posts)

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Mathematics as a concept—not even a discipline, though that too—is one of those things that is both science but also magic at the same time.

Science, because, d’uh, but magic because just look at the kind of mind-boggling shenanigans you can get into by simply assuming that one divided by three is one third, and one third is 0.(3) and times 3 it’s 0.(9). Who Houdinied that extra 0.(1) away?!

But outside the wonder that this scientific “logic” provides, it’s pretty much useless. And you bet there’s a dedicated community around useless math online—well, useless, but interesting.

#1 One 9 Inch Pizza vs. Two 5 Inch Pizzas

GuvSingh

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195points

#2 How Tall Would This Tree Have Been, And How Visible Would It Have Been?

"So the ave stump height is cut to 0.45 m. Let's assume an oak, with an ave height of 20m. Thats about 2.3% of overall height.

This tree would therefore be around 11.7km high using that ratio. Almost high enough to tickle the stratosphere at 12km

So if I used the horizon calculator right, you could still see the bastard 387km away

EDIT: Just to answer a few of the many questions. In American that'd be about 7.3miles, or 13,760 washing machines"

BrightInsight6

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125points

#3 A Natural Headache Cure

AlanPlotzker

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112points

So, there’s a community on Reddit called r/TheyDidTheMath, which captions itself as “useless, yet interesting calculations.” The description smugly points out “and they said math has no real world applications.”

The subreddit is ranked in the top 1% on the platform and boasts 1.4 million members.

#4 What Does His Shirt Say

"The quote is "I'm sexy and I know it"

sqrt(1+tan^2) can be verbalized as "sec" and so this formula is the "sec of c"

"I'm sec C and I know it""

tabanopro

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90points

#5 Is This True?

"They’re called crinkle crankles. A single leaf wall over that distance would need brick piers approx every 1.5-2m if it was a retaining wall it would need to be at least 9” wide (2 bricks). The crinkle crankle has more strength due to it’s curved nature so can be 4” wide or a single leaf of bricks.

For the maths if we can assume they’re true semi-circles then each semi circle would be 1/2piD or 1.57D whereas a double leaf wall would be 2D for the same length D

Therefore using 21.5% less bricks than a double leaf wall"

stem_feed

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84points

#6 Approximately How Large Would The Car Have To Be In Order To Be That Curved?

"Quick eyeballing suggests a curvature of about 30°; that's 1/12th of a full circle, so given that the Earth's circumference is just over 40,000 km, the car would have to be about 3333 km long, or about the driving distance from Chicago to Los Angeles, or about 5.5 million washing machines (in case you're too American to understand kilometers)."

CrazyPotato1535

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84points

You can say the subreddit deals in very situational and contextual math where you’d probably only be able to use it in very niche cosmological occasions.

Like calculating the amount of toilet paper you’d need for 14 days of quarantine. Or what all the humans as fine goo would look like in Central Park. Or the number of small pizzas you’d need to substitute a large pizza. OK, that last one sounds useful.

#7 How Much Does This Kitten Weigh?

"One source says the “minimum actuation force” of a key is 47.6 grams. If we assume the kitten is standing on 4 keys (only one per paw) 4*47.6 is 190.4 grams or 0.4 pounds. Ao the kitten would be under that weight. It appears that the kitten is standing on more than 4 keys though so maybe 1/2 pound."

g-amefreak

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80points

#8 Really Though, How Much Different Exactly?

"$9.33 on the left and $21.51 on the right"

destructorrobot

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79points

#9 How Many Combinations Of 9 Ingredients Are Possible. Using All 9 At Once Is Not Required

"Each ingredient can either be included or not -- that's 2 possibilities. Multiply out all 9 ingredients and we have 29 = 512 in total. I presume you'd want to exclude the 1 possibility where none of the ingredients are included, so that leaves 511."

gracecamille_

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75points

Bored Panda has reached out to the founder of the subreddit, r/FragTheWhale, who was more than happy to tell us more about r/TheyDidTheMath.

"I was a part of the tool subreddit, r/toolband, and someone had made an actual calculated, in-depth analysis of a Tool lyric 'slide a mile six inches at a time on Maynard's [ding-dong]' and what length of time it would take," elaborated Frag. "Loved the idea so much, I created a subreddit for it with 1.54 million subs!"

#10 Is This True And If Yes How Deos It Work?

"Quite the opposite, it will leave you with less sandwich. Since no cut is perfect, some of the sandwich molecules will stay on the knife or there is more crumbs on the cutting board. Therefore, cutting on a diagonal (longest cut) will dislodge more material of the sandwich than cutting along shorter line"

PleaseBeGneiss

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66points

#11 How Much Would This Actually Cost?

"Return flight JFK - Madrid: ~€750 Minimum income in Spain: €850/mo; 24 months amount to €20400. We'll assume that since a lot of people in Spain have to make do with this much, you will figure it out too. Learning Spanish is pretty straightforward, if you live in Spain for 2 years, you're practically guaranteed to pick up enough of it to get by, but let's say you spend €100 on a couple textbooks and a dictionary, just to get you started. Depending on where in the US you live, there might even be a solid chance that you already speak the language, after all it's the country's second language, with more speakers in the US than in Spain. You will also be spending a bit on visas and other bureaucratic requirements, let's call that another €200. Running with the bulls and getting trampled can be had for free. And then there's the hip replacement itself, at $7,371, or €7074. However, depending how you play it, you could actually take a minimum-wage job in Spain, and qualify for public healthcare, in which case the hip replacement might actually be covered. But let's just assume you have to pay for it out of pocket (which, frankly, is a pretty unusual thing in Europe, and typically only happens when people have to get treatement abroad and the insurance situation hasn't been figured out, or for a couple religious weirdos who object against having health insurance on moral grounds).

So let's ring you up; grand total: €28524, that's about $29700.

Not only does it fit comfortably into the US figure, you even have some $12,000 to spare"

ElonsBeans

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64points

#12 What Is A Penguins Slapping Power?

"The average emperor penguin slaps with about the same force as a middleweight boxer. 800-1000 PSI"

CreativeName6574

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58points

Despite the tagline "useless math", the subreddit actually serves an important educational function.

"I think it can serve an educational purpose! Especially in terms of shifting perspectives or addressing myths (something about too many bananas are bad for you? Turns out, you'd have to eat like 4,000 bananas in a day to overdose on potassium, something like that). Initially, people kinda used it as a tool to get others to do their math homework for them."

#13 I’ve Always Wondered How Much Money Walt Actually Had

"Assuming those are $100 bill stacks at $10,000 each. I count 12 stacks across and 15 stacks deep and assuming that each stack is ~0.5 inches tall with a total height of ~30 inches.

12 * 15 * (30 / 0.5) * 10,000 = $108 Million dollars."

Danny13oyy

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57points

#14 A Lot Of Paper, But How Much

"36,567,729 sheets of letter sized paper according to Excel (single sided)

According to Google a pallet contains 200,000 sheets

Therefore 182 pallets of paper would be needed.

A photocopier can apparently print 500,000 sheets in its lifetime, so you would need 73 photocopiers"

noideaman69

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57points

#15 How Many Rocks Would This Person Have To Throw To Flood Denmark?

"The total area of ocean is about 361 million square km, or 3.61 x 1014 square meters.

The highest point of Denmark is about 171m.

The earth is large enough that we can choose to ignore the curvature over a change of radius of 171m (compared to the radius of 6300km it’s less than a rounding error).

What we can’t ignore is that there is about 30 million square km of land that is 171m or less above sea level which will also be flooded (estimating from a hypsographic curve). I’ll factor in a mean of half of that to give the new earths surface figure of 3.76 x 1014 square meters.

This means that there would need to be 171 x 3.76 x 1014 = 6.43 x 1016 cubic meters of water displaced.

If we assume a good throwing rock has a volume of 1 litre, then you would need 6.43 x 1019 rocks.

At 1 rock per day that’s going to be 1.76 x 1017 years, or 12 900 000 times the age of the universe.

If all 8 billion people on the world threw one rock per second, it would only take 250 years"

stretch_armstrong_

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56points

When asked what the community is like, OP explained that it's hard to say for sure as they have taken a step back from Reddit as a whole. But, the community seems to thrive all the same, and, over the years, Frag noticed that there are essentially two camps of people: the crowd that's all about silly humor in math, and the crowd that's all about hardcore science and analytics.

It goes without saying that it is very entertaining to see people take silly discussions both seriously and scientifically.

#16 How Many Nickels Would It Take To Crush You?

"According to a google search, it takes about 4,000 newtons to crush a bone, & I’m going to assume that an average person has a frontal surface area of 1 m2 for ease.

A nickel weighs 5 grams, which equates to about 0.05 newtons of gravitational force… you’d need at least 81,578 nickels on top of the person, or about $4,078.90"

ropermarisa

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56points

#17 What Are The Odds?

"Beginner: 1 in 102 million
Intermediate: 1 in 6.1 million
Expert: 1 in 477,000"

SMOKE1798

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53points

#18 How Much Would This Cool The Tea?

"Oh come on this is doable from an engineering point of view:

One sip per second of 10ml (a shot glas' equivalent in a few seconds)

90°C tea, 0°C water (I see ice?), ∆T =90

Conduction in the thin straw is negligible, basically water-to-water heat transfer at a slow rate: the convection coëfficiënt for that is about 1000W/m²K (forced convection water to unforced water essentially)

Straw is 5mm diameter, 150mm length is submerged. Total area = 5π*150 = 2350mm² heat exchange area.

As such, the heat (power) transferred per second is = 9010002350/1e6 ≈ 211W

211W for 0.01kg water (tea) per second is ∆T = 211/4200/0.01 ≠ 5°C difference.

This matches my experience: the straw is simply not big enough to offer proper area for heat exchange:

Source: 10 years of steam boiler engineering

Hope you enjoyed!"

CEO_Of_Rejection_99

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50points

When asked about any favorite posts on the subreddit, the founder noted that it's hard to pick out a favorite. Whenever they pop on to the subreddit, it feels like everyone is still staying true to what the subreddit originally was and stood for nearly a decade back.

#19 How Fast Would You Need To Go To Successfully Complete The Loop?

"Im gonna assume the loop is about 60m based on the height of the building next to it.

At the top of the circle, the two forces are mg and centripetal force. The two together equal ma (a being v2/r.) So mg + Fc = m(v2/r). Set Fc to 0 as you would have to have a centripetal force slightly above 0 to complete the loop. This gives us v2 = sqrt(gr). For a 60m loop (30m radius) v = 17.1m/s.

This is the speed at the TOP of the loop. Using conservation of energy, we can say that 1/2mv2 + mgh = 1/2mv2 (the first part is top of loop, second part is bottom of loop). Cancel m and plug in numbers.

You would have to travel 38.34m/s or 138kph (85.7mph) to make the loop."

darthbane911

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48points

#20 If The Sun Turned Into A Black Hole Of Equivalent Mass, Would The Accretion Disk Disk Be Large Enough To Destroy The Earth? If Not, How Bright Would It Be?

If The Sun Turned Into A Black Hole Of Equivalent Mass, Would The Accretion Disk Disk Be Large Enough To Destroy The Earth? If Not, How Bright Would It Be?

"NASA did the math on this

"If the Sun was replaced with a black hole that had the same mass as the Sun, the Schwarzschild radius would be 3 km (compared to the Sun's radius of nearly 700,000 km). Hence the Earth would have to get very close to get sucked into a black hole at the center of our Solar System.""

Valdevia_Art

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47points

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