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Math Formulas Everyone Should Know

Updated on January 13, 2016
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TR Smith is a product designer and former teacher who uses math in her work every day.

Two giraffes discussing the Navier-Stokes equation. (Image courtesy of Pixabay)
Two giraffes discussing the Navier-Stokes equation. (Image courtesy of Pixabay)

What good is it to know how to find the derivative of a cubic polynomial or how to calculate the squared sum of the cubes of the first 500 prime numbers? If you can't figure your age in giraffe years, or the amount of Velveeta cheese you need to host a wrestling match, you haven't learned real mathematics. Here are eleven essential lessons and formulas for the real math you were never taught in school, but should have been!



Number of Days You Can Wear the Same Pair of Underwear

The number of consecutive days you can wear the same pair of undies is inversely proportional to your Stank Index (SI). To calculate your Stank Index...

  • Start with the number 12
  • Subtract 1 for each day of the week you shower.
  • Add 1 for every day you do moderate exercise.
  • Add 5 if you are male.
  • Subtract 2 if you wear deodorant every day.
  • Add 1 if you eat Velveeta.
  • Subtract 2 if you are a diligent wiper who uses almost a whole roll of TP.

Tally your points to get your Stank Index. The higher the number, the more stank you got.

The number of days in a row you can wear the same pair of underwear is 15 divided by your Stank Index, rounded up to the next whole number. For example, if you're a relatively clean individual with SI = 3, then you can wear the same pair for 5 consecutive days since 15/3 = 5. If your SI = 17 you can only wear a pair of underwear once, since 15/17 = 0.88, which equals 1 when rounded up.



How to Calculate Your Age in Giraffe Years

The lifespan of a giraffe in the wild is around 25 years, and typical giraffe reaches reproductive maturity at around age 5. For humans, life expectancy is about 80, with reproductive maturity at about age 14. Using this data you can equate the number of human years you've lived to an equivalent number of giraffe years. If your current age in human years is A, then the formula to convert to giraffe years is

5A/14, if 0 ≤ A ≤ 14

(10A + 25)/33, if 14 ≤ A.

For example, a 10-year-old human child is 50/14 ≈ 3.5 years old in giraffe years, while a 57-year-old human adult is (10*57+25)/33 ≈ 18 years old in giraffe years. Use this fascinating factoid as an ice-breaker the next time you're at a gathering of African ruminants.



How to Calculate Your Age in Martian Years

With advances in space exploration comes the possibility of humans living on Mars. Mars orbits the sun completing one full revolution every 16,488 hours, while the Earth makes one revolution around the sun every 8,766 hours. Since 8766/16488 = 0.53166, an Earth year is only 53.166% of a Martian year. Thus, to calculate your Earth age in Martian years, you simply multiply it by 0.53166.

For example, if you are 43 years old on Earth, you are only about 23 years old on Mars. Break out the mini skirts, tank tops, and acid-washed skinny jeans. You've still got about 7 more Martian years until you're too old to be dressing like a teenager.

Westward view from a Martian plateau. (Image courtesy of NASA)
Westward view from a Martian plateau. (Image courtesy of NASA)

The Love Calculator Formula

Doing the "love calculator" is the ancient art of divining whether you have a better chance of going out with Robert from second period chemistry, or Kyle from seventh period English.

Euclid "McLovin" of Alexandria was an ancient Greek mathematician who devised the love calculator formula. (Image courtesy of Wikimedia Commons)
Euclid "McLovin" of Alexandria was an ancient Greek mathematician who devised the love calculator formula. (Image courtesy of Wikimedia Commons)

To calculate the percent chance of marrying your crush, first you count the number of letters in your full name, the number of letters in your crush's full name, then multiply those two numbers. Next, you count the number of distinct alphabet letters that are common in both of your full names, ignoring repeated letters because that's way too hard. Add this number to the number you got before. Finally, look at the last two digits. This is your love match percentage.

Example: You are Mary Marie Martin and the object of your affection is Walter Wallis Walkerson. You have 15 letters in your name and he has 21 letters in his, which gives you 15*21 = 315. There are six letters common to both of your names (A, E, I, N, R, T), which gives you 315 + 6 = 321. The last two digits are 21, so you only have a 21% chance of walking down the aisle with Walter.

On the other hand, Mario Miguel Martinez is looking good at 92%.



Number of Toddlers You Could Take on in a Fight

A toddler is a person so amped up with no regard for the rules of polite society that she's not even allowed to go to school; a toddler has to be under adult supervision non-stop for the protection of others. You do not want to take on one of these creatures in a fight if you don't have to.

But if you did have to fight a toddler, how many could you takcle? Use this secret formula derived by ancient Chinese mathematicians:

(W + H)/5 - A/2 + X

where W is your weight in pounds, H is your height in inches, A is your age in (human Earth) years, and X is your bad-ass factor. Score X = 0 to -5 if you are a wuss, or X = 1 to 5 if you are a between-naps fighting machine.

Example: A 120-pound, 28-year-old woman who is 60 inches tall with a bad-ass factor of 3 can take on 25 toddlers in a fight as

(120 + 60)/5 - 28/2 + 3 = 25.



How Much Velveeta and Milk You Need for Cheese Wrestling

Velveeta is an odorless, tasteless food product made by blending lard, latex paint, and orange cheese powder found in boxes of Kraft Mac&Cheese. Paradoxically, orange cheese powder is dehydrated Velveeta. There is only one way to serve and eat Velveeta: with shame.

We can use simple math to calculate the amount and Velveeta and milk you need to make enough cheese sauce for an exciting match of cheese wrestling. Let T be the capacity of your wrestling tank in gallons, and N be the number of cheese wrestlers. The number of 32-oz. blocks of Velveeta (V) and gallons of milk (M) you need are given by the equations

V = 2*T + 30*N

M = V/24

For example, if you have 4 wrestlers who are fighting in a hot tub that holds 750 gallons, then you need 2*750 + 30*4 = 1,620 blocks of Velveeta, and 1620/24 = 67.5 gallons of milk. The wrestling sauce is prepared by adding 2/3 cups of milk to every melted block of Velveeta.



Number of People Who Have Lived on Earth Before You

The Earth's current human population is over 7 billion, and scientists estimate the number of people who have ever lived on Earth is about 108 billion. How many humans were born before you were? The answer depends on the estimated birth rates from 50,000 BC to the present day and your birth year.

Let the variable Y be the year of your birth. Select the year range of your birth from the list of formulas below, and plug in the value of Y into the corresponding formula. The number you get is the approximate number of people who have lived before you.

Born between 1900 and 1950:
96654876954 + (1950-Y)*67803965

Born between 1950 and 1995:
100045075169 + (1995-Y)*120606778

Born between 1995 and 2011:
105472380169 + (2011-Y)*133145477



Number of Cats You'll Die Alone With

it's a curious fact of the human condition that people who die alone die surrounded by cats. Just how many cats depends on the degree of loneliness. Use this handy guide to predict the number of feline companions you'll have.

Chillin' cat,  waiting for you to die. (Pixabay)
Chillin' cat, waiting for you to die. (Pixabay)
  • Start with the number 3.
  • Subtract 2 if you are under 50, subtract 3 if you are under 35.
  • Subtract 2 if you are married, subtract 1 if you were married.
  • Add 1 if you can crochet or knit, add 2 if you can do both.
  • Add 2 if your favorite article of clothing is socks.
  • Add 2 if your able to find a grammatical error in this sentence.
  • Add 2 if you are female.
  • Add 1 for every variety of tea you can name.

Tally your points to discover how many cats you'll have at the end. If you end up with a negative number, take its absolute value and add 14 to get your cat number.



Number of Licks to Get to the Center of a Tootsie Pop

The number of licks you take before caving in an biting a Tootsie Pop is a function of your age, A, and your impulsiveness factor, X. Rate yourself on a scale of 1 to 10, where X = 1 if you are calm and calculated, and X = 10 if you are highly impulsive.

The number of licks it takes to get to the center of a tootsie pop is 2A/X. Round this number up to the next whole number if you get a fraction or decimal.

Example: Mary is a 25-year-old with an impulsiveness factor of 6. Since 2*25/6 = 8.33, she will take 9 licks before giving up and just biting the sucker.



How to Set the Thermostat to the Right Temperature

Thermostat wars are the second leading cause of divorce during winter and the third leading cause of roommates moving out mid-lease. Use this guide to find your ideal house temperature, and then average the results of all the people in the house who pay the heating bill. The average is the household ideal temperature that everyone can live with.

  • Start with the number 68 degrees Fahrenheit.
  • Subtract 1 degree for every 10 pounds overweight you are, and add 1 for every 10 pounds underweight you are.
  • Add 2 degrees if you have penchant for walking around naked.
  • Add 2 degrees if you like seeing your housemate(s) naked.
  • Subtract 1 if you look good in sweaters and you know it.
  • Subtract 1 if you cook with the oven/stove at least twice a week.
  • Add 2 if you believe lack of money should never interfere with comfort.


For example, if three roommates Dwight, Dwayne, and D'William have ideal temperatures of 67, 71, and 68 degrees, then the thermostat should be set to 68.7 degrees, the average of these three temperatures.


Probability of Winning the Lottery

Knowing how to compute the probability of winning the lottery is crucial to responsible financial planning. Most textbooks show you how to compute lottery odds with math functions that take up several lines. But the truth is you can calculate it with a pencil and paper, or a pocket calculator, using this easy one-line equation:

(7 - 7) x (8 - 8) + (3 - 3)

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    • CWanamaker profile image

      CWanamaker 3 years ago from Arizona

      Simply Awesome. I love it!

    • calculus-geometry profile image
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      TR Smith 3 years ago from Eastern Europe

      Thanks! I decided not to include the more X-rated math applications.

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