# How do you use math as an adult? **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [January 18, 2020, 2:06pm UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618 "2020-01-18T14:06:42Z")\ **Posts on this page:** 20\ **Page:** 4
**Author:** ![robardin](https://avatars.discourse-cdn.com/v4/letter/r/43a26b/32.png) [@robardin](https://boards.straightdope.com/u/robardin)\ **Post date:** [January 21, 2020, 3:50pm UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618/61 "2020-01-21T15:50:42Z")
> [@CelticKnot](#): > > Discussing math with a student, it occurred to me that “You’re going to need this when you grow up” may have been an exaggeration. **Other than working in STEM fields, how much of high school math do you use in your everyday life?** _The main reason to learn “higher” math (beyond arithmetic or simple fractions) is for “numeracy”_, a sense of what is actually right, and a feeling for the right way to think about something if you want to get to the right answer. But in terms of “high school math”, the #1 thing I use from that aside from work are from probability, counting, and combinatorics, as applied to playing games. And understanding of how compounding works (as with paying or receiving interest) is pretty important to understand why thinking in terms of “can I afford my monthly payment” is a debt trap lenders are eager to profit from. In both cases it’s not usual that I have the time to sit down and “do the math” to come out to an exact answer in real time, but simply having done that exercise enough times that my “feel” for what’s going on is much better than most people’s naive understanding. A lot of people, when dealing with some kind of random choice, kind of just assume things are “about 50/50?” in odds. What has also proven useful, again not necessarily sitting down and doing the math every time but just having internalized the concepts, is understanding the different kinds of means (averages) - specifically, harmonic mean vs. arithmetic mean (straight average). For example, a lot of people get speed (miles/hour) or fuel economy concepts wrong (miles/gallon) because they use the wrong denominator when computing an average to track or to compare things, because they’re not actually thinking about what the rates mean but are “just manipulating numbers like any other numbers” - following numerical recipes, which is “shallow math” and not “actual math”. For example, if you drive to a point 25 miles away at a steady 50 MPH and then came back at 100 MPH, what was your average speed for the round trip? No, it’s not (100+50)/2 = 75 MPH, even though the distance both ways is obviously the same, because the rate is “per hour” (in time), not “per mile” in distance. You drove 25 miles at 50 MPH, which means it took you 30 minutes; and then drove 25 miles back at 100 MPH, which took you 15 minutes. So you drove a total of 50 miles in 45 minutes, which is 50 miles / 45 minutes \* 60 minutes per hour = 66.67 MPH. Which is what the “harmonic mean” computation would give you. Now, if you’d driven 30 MINUTES at 50 MPH and then 30 MINUTES at 100 MPH, then your average speed would indeed be 75 MPH, the straight average. Because the denominator is now the same concept as the rate (the time not the distance). You don’t have to remember how to do a harmonic mean off the top of your head (it’s a spreadsheet function for me), the important bit is to realize when you SHOULDN’T use a straight arithmetic average. And the critical thing to learn in high school math is that if your answer was right, you can check it by plugging it back in. Was your average speed, in fact, 75 MPH? Computing the time you actually took to make the round trip immediately makes it obvious you’ve done the wrong thing. So if you aren’t sure if you’re making a “wrong average method” error, you can easily find out. ---
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [January 21, 2020, 4:54pm UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618/62 "2020-01-21T16:54:47Z")
Latest use of math not related to my job: figuring out the best direction to place solar panels. Start with geometry of the earth’s orbit and rotation, then other things like panels shading each other. I used vectors, but I’m sure it’s doable with traditional geometry. > [@peccavi](#): > > This is a trap that engineers fall into. If you don’t have an understanding of the math behind the tables, you risk ending ups with a slipped decimal place, a slightly off conversion, or a just plain wrong answer that you have no way of applying a simple “sanity check” to. > > Based on my degrees, I’m an engineer and a physicist. One thing from physics I brought to engineering is to always have some expectation (or bounds) of the answer you should get. If the table, calculator, simulator, etc. produces an answer that is significantly off, you need to do some double checking. I’ve seen many a bombed design review when someone in the back of the room (sometimes me) does a back of the envelope calculation and asks why the numbers being presented are so far off from what a rough approximation would expect. Quoted for emphasis. Working with numbers gives you a feel for numbers, which even if you don’t know the right answers, at least you’ll be asking the right questions. ---
**Author:** ![sitchensis](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sitchensis/32/4892_2.png) [@sitchensis](https://boards.straightdope.com/u/sitchensis)\ **Post date:** [January 21, 2020, 6:21pm UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618/63 "2020-01-21T18:21:38Z")
I’m a forester. When cruising timber I use trig to calculate tree heights. I use statistic because those trees are part of plots, and I need to calculate sample intensity, total volume and variability/error. I use that data to do appraisals, which incorporate selling value by species minus costs, including stump to truck costs, hauling, profit and risk, road use fees, scaling etc. I design logging roads, and calculate cut and fill, bridges and bridge abutments, slopes and turning radius. I convert between slope distance and ground distance when laying out stream buffers. I occasionally use coordinate geometry and can plot and find UTM and latitude and longitude coordinates. I convert between map distance and ground distance. I use just about everything I was ever taught. My field is really STEM heavy, but that’s not what students entering my field think. ---
**Author:** ![Zyada](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zyada/32/3028_2.png) [@Zyada](https://boards.straightdope.com/u/Zyada)\ **Post date:** [January 21, 2020, 10:26pm UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618/64 "2020-01-21T22:26:23Z")
I’m a programmer, so word problems are basically what I do for a living. Someone tells me what they know and what they want to know, and it’s my job to figure out how to get from the beginning to the end. I let the computer do the math, but I have to figure out what math the computer will do Also, I’ve used c=2πr to make circle skirts for myself. Are you trying to give them new problems that you feel might be more relevant, or are you just trying to justify teaching math to them, or to yourself? Or just wondering if people actually use math? To me, the real reason why math is needed is the same as why football players run through paths of tires. You never find tires on the playing field, but it builds muscles that help the players when they’re on the field. So you may never actually consciously use math (except, hopefully things like sanity checks on money transactions, etc.), but you’re using mental muscles built by your math lessons to do things better. ---
**Author:** ![turner](https://avatars.discourse-cdn.com/v4/letter/t/22d042/32.png) [@turner](https://boards.straightdope.com/u/turner)\ **Post date:** [January 22, 2020, 12:05am UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618/65 "2020-01-22T00:05:08Z")
> [@JohnT](#): > > I remember _detesting_ having to learn matrix math, just hated it. Wondered when I will ever, ever put calculations in f-in tables, and why I was being taught something I would never, ever use. > > Now? Now I use it all the time in creating spreadsheets. Go figure. See this is the problem I have with how many talk about education in general these days. “I’m never going to use that” says the high school freshman who doesn’t have the slightest clue of what they will be doing in 10 years. I wanted to be an architect. Now I’m in charge of building, commanding and controlling satellites. I became more interested in building things rather than buildings, so I decided to be an engineer. Different skill set. Similarly I know a lot of liberal arts majors who are now in IT. By stopping math at “checkbook balancing” which I learned in like sixth grade, or not teaching the sciences, history or art, you close a lot of doors to opportunities and potential interests that a student might not know about, but might find interest in once exposed. ---
**Author:** ![Kropotkin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kropotkin/32/18045_2.png) [@Kropotkin](https://boards.straightdope.com/u/Kropotkin)\ **Post date:** [January 22, 2020, 1:15am UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618/66 "2020-01-22T01:15:39Z")
> [@CelticKnot](#): > > They’re second graders. They don’t have real world experiences. Most of them are struggling with regrouping, and some don’t even know one-to-one correspondence yet. > As for the tutoring, I have to teach what the company provides or help them with their homework. I don’t write lesson plans. > > So, for sine and the quadratic equation, no, they’re not needed in adult life. They actually do have real world experience and questions. I suspect they could come up with all sorts of ideas and questions that require math. It’s hard to teach when you can’t write the lesson plan…my sympathies! ---
**Author:** ![Jaguars](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jaguars/32/5879_2.png) [@Jaguars](https://boards.straightdope.com/u/Jaguars)\ **Post date:** [January 23, 2020, 2:09am UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618/67 "2020-01-23T02:09:38Z")
You don’t think of using a tape measure as maths until you have to teach multiple adults how to read one. Everyone will end up using one at some point. ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [January 23, 2020, 2:44am UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618/68 "2020-01-23T02:44:40Z")
> [@Jaguars](#): > > You don’t think of using a tape measure as maths until you have to teach multiple adults how to read one.\*\* Everyone will end up using one at some point.\*\* I go to great lengths to _not_ use one. ---
**Author:** ![Chefguy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chefguy/32/138_2.png) [@Chefguy](https://boards.straightdope.com/u/Chefguy)\ **Post date:** [January 23, 2020, 3:22am UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618/69 "2020-01-23T03:22:36Z")
> [@Jaguars](#): > > You don’t think of using a tape measure as maths until you have to teach multiple adults how to read one. Everyone will end up using one at some point. Major PITA. I had to do this for young electrician students in the Navy. It was painful watching one guy lying on the ground on his stomach, tape measure stretched out along a piece of conduit, while he laboriously ticked off 1/16" increments. ---
**Author:** ![Balthisar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/balthisar/32/2825_2.png) [@Balthisar](https://boards.straightdope.com/u/Balthisar)\ **Post date:** [January 23, 2020, 6:41pm UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618/70 "2020-01-23T18:41:47Z")
Leaving out my occupation in a STEM field, math is useful all the time. Cooking. Car-related. Anything finance. Property ownership. Tax rates. Travel and leisure. Budgeting. Hobbies such as woodworking. These all use arithmetic, algebra, trig, and even calculus. No, I’m not doing things like computing rates of change manually; but I know how to do so, and know why it works, and so have trust that I’m doing it correctly when plugging formulas into Excel. ---
**Author:** ![Yllaria](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yllaria/32/3452_2.png) [@Yllaria](https://boards.straightdope.com/u/Yllaria)\ **Post date:** [January 24, 2020, 2:57pm UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618/71 "2020-01-24T14:57:58Z")
My DIL does taxes, in the season. She’d make less if more people could do their own. Although, sadly, a lot of people who pay to have simple taxes done are doing it to get ~90% of their refund now, rather than having to wait for it. As in, they’re paying a fee and 10% of their refund to get the rest now. I don’t think that’s a problem with math, exactly. ---
**Author:** ![P-man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/p-man/32/3606_2.png) [@P-man](https://boards.straightdope.com/u/P-man)\ **Post date:** [January 25, 2020, 12:23am UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618/72 "2020-01-25T00:23:37Z")
> [@Chefguy](#): > > Major PITA. I had to do this for young electrician students in the Navy. It was painful watching one guy lying on the ground on his stomach, tape measure stretched out along a piece of conduit, while he laboriously ticked off 1/16" increments. Really? I bombed algebra, and was a so-so geometry student. I knew how to use a tape measure before I was in school; I would take the one out of my dad’s junk drawer and measure things to my heart’s content. Whatever family member I asked told me what the marks meant. I didn’t have a good handle on fractions beyond a quarter until second grade or so, but using a tape measure ranks pretty high on the list of easiest things for me to learn. ---
**Author:** ![jtur88](https://avatars.discourse-cdn.com/v4/letter/j/e9c0ed/32.png) [@jtur88](https://boards.straightdope.com/u/jtur88)\ **Post date:** [January 25, 2020, 10:19am UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618/73 "2020-01-25T10:19:53Z")
Americans are in a special, unique position. We have to use math daily, to convert the weights and measures that are uniform in the rest of the world. I’ve found it very useful to know how to convert quickly in my head. Traveling, I do a lot of currency conversion, too. It would never occur to me to reach for a phone to do math that 'i can do pretty well in my head. ---
**Author:** ![CelticKnot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/celticknot/32/3392_2.png) [@CelticKnot](https://boards.straightdope.com/u/CelticKnot)\ **Post date:** [January 25, 2020, 4:27pm UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618/74 "2020-01-25T16:27:10Z")
Does any Doper use the Quadratic Equation for anything? ---
**Author:** ![Thudlow\_Boink](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/thudlow_boink/32/320_2.png) [@Thudlow\_Boink](https://boards.straightdope.com/u/Thudlow_Boink)\ **Post date:** [January 25, 2020, 5:07pm UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618/75 "2020-01-25T17:07:34Z")
> [@CelticKnot](#): > > Does any Doper use the Quadratic Equation for anything? Do you mean **a** quadratic equation, or **the** Quadratic **Formula**? A quadratic equation is a particular type of algebraic equation, of which there are many specific examples. The Quadratic Formula is a formula that gives the solutions to any particular quadratic equation. Both do come up in higher-level math and other STEM fields (e.g. problems involving projectile motion), but you asked for “other than working in STEM fields” in your OP. Offhand I can’t think of an application to non-STEM “everyday life,” but I would be interested in hearing what, if anything, other Dopers do use quadratic equations and/or the Quadratic Formula for. [Here’s one page I found](https://www.mathsisfun.com/algebra/quadratic-equation-real-world.html) of “real world examples of quadratic equations.” They may be the kind of thing you’re looking for, or you may find them too contrived or artificial or STEM-y. ---
**Author:** ![Tripler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripler/32/21807_2.png) [@Tripler](https://boards.straightdope.com/u/Tripler)\ **Post date:** [January 25, 2020, 7:20pm UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618/76 "2020-01-25T19:20:33Z")
I’m an Engineer, and use math on a daily basis. Sometimes simple algebra, sometimes a li’l calculus, sometimes generating or interpreting statistics. I’m actually taking Calculus over again, as per-requisites for another Engineering degree. Tripler I just re-started Calc II. ---
**Author:** ![Kron](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kron/32/12444_2.png) [@Kron](https://boards.straightdope.com/u/Kron)\ **Post date:** [January 26, 2020, 1:50am UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618/77 "2020-01-26T01:50:15Z")
Surveyor/mapper for work, programmer/computer nerd for fun. I math a lot. Rarely a day goes by that of course algebra of some sort isn’t being used. I use sines/cosines often for converting distances from angled measurements to cardinal distances for proportional calculation of missing monuments. As a general rule, we work in decimal feet for measurements, but often engineers provide plans in architectural units (what we call using fractional inches) so I do a lot of conversions back and forth, as well as from metric to US Survey Feet. I also do a lot of simple coordinate geometry, so Pythagoras is a hero to me. ---
**Author:** ![jtur88](https://avatars.discourse-cdn.com/v4/letter/j/e9c0ed/32.png) [@jtur88](https://boards.straightdope.com/u/jtur88)\ **Post date:** [January 27, 2020, 1:38am UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618/78 "2020-01-27T01:38:41Z")
When I lived in Chile I had none of my usual resources (no internet then) so I had to create my own star charts, using a table of star coordinates found in a dog-eared old World Almanac. And I had a view of the Pacific, so I worked out my own formula for determining the distance to the horizon based on height of the observer. Those are few examples, but the point is, I could do it. ---
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [January 28, 2020, 4:37am UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618/79 "2020-01-28T04:37:42Z")
> [@Senegoid](#): > > Knowing that the population of this Board consists of literate and numerate people, I’ll take it as a given that everyone here knows of the book [**Innumeracy: Mathematical Illiteracy and Its Consequences** by John Allen Paulos](https://www.goodreads.com/book/show/186749.Innumeracy). > > ETA: He begins with this thought-problem that he likes to give students: Estimate how fast your hair grows, _in miles per hour_. The point being, he finds that a lot of students have no concept that hair growth can even be measured in miles per hour. I met Paulos many years ago and have an autographed copy of the book. Shortly after reading it, I calculated the speed at which my fingernails grow in mph. (Much easier to do than hair. Trim your nails all the way down, wait a month, measure the length.) I found it to be about 1/4 inch per month, or about 5.5 billionths of 1 mph (8.8 billionths of 1 kph). Doing that exercise gave me a much clearer insight into just how big a billion is. A mile is a large (on the human scale) but fairly comprehensible unit of measure. If you asked most people to show you with their fingers how much a billionth of a mile is, I’ll bet a lot of them would hold thumb and forefinger maybe a half or a quarter of an inch apart. But that’s way too much for even a _millionth_ of a mile, which is a tiny bit more than 1/16th of an inch. One billionth of a mile is 1/1000th of 1/16th of an inch. And every hour, my fingernails grow 5.5/1000ths of 1/16th of an inch. ---
**Author:** ![Tripler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripler/32/21807_2.png) [@Tripler](https://boards.straightdope.com/u/Tripler)\ **Post date:** [January 28, 2020, 1:52pm UTC](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618/80 "2020-01-28T13:52:02Z")
> [@Kron](#): > > Surveyor/mapper for work, programmer/computer nerd for fun. > … > I also do a lot of simple coordinate geometry, so Pythagoras is a hero to me. Oh boy howdy to I have questions for _you!_. Tripler We’ll have to share a cup of coffee some time. [Previous page](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618.md?page=3) [Next page](https://boards.straightdope.com/t/how-do-you-use-math-as-an-adult/846618.md?page=5)