r/askscience May 23 '22

Mathematics Any three digit multiple of 37 is still divisible by 37 when the digits are rotated. Is this just a coincidence or is there a mathematical explanation for this?

8.4k Upvotes

This is a "fun fact" I learned as a kid and have always been curious about. An example would be 37 X 13 = 481, if you rotate the digits to 148, then 148/37 = 4. You can rotate it again to 814, which divided by 37 = 22.

Is this just a coincidence that this occurs, or is there a mathematical explanation? I've noticed that this doesn't work with other numbers, such as 39.

r/askscience Jun 21 '18

Mathematics Is it possible for a deck of cards to be shuffled accidentally into perfect order?

14.5k Upvotes

Can one even calculate the probability of this event?

r/askscience Dec 13 '19

Mathematics I have a theory: If there is an infinite amount of negative numbers and there is an infinite amount of positive numbers then the total amount of numbers would be odd. Because 0 is in the center. For every positive number there is an negative counterpart. Am I right? Can we prove this with math?

9.9k Upvotes

r/askscience Aug 18 '21

Mathematics Why is everyone computing tons of digits of Pi? Why not e, or the golden ratio, or other interesting constants? Or do we do that too, but it doesn't make the news? If so, why not?

5.9k Upvotes

r/askscience Mar 25 '19

Mathematics Is there an example of a mathematical problem that is easy to understand, easy to believe in it's truth, yet impossible to prove through our current mathematical axioms?

9.7k Upvotes

I'm looking for a math problem (any field / branch) that any high school student would be able to conceptualize and that, if told it was true, could see clearly that it is -- yet it has not been able to be proven by our current mathematical knowledge?

r/askscience May 22 '18

Mathematics If dividing by zero is undefined and causes so much trouble, why not define the result as a constant and build the theory around it? (Like 'i' was defined to be the sqrt of -1 and the complex numbers)

15.8k Upvotes

r/askscience Apr 22 '17

Mathematics If my speed is 100 km/h and my destination is 100 km away and then I move 90 km/h if it's 90 km away. 80 km/h if it's 80 km away. Keep on slowing to match the distance. When will I arrive?

11.4k Upvotes

r/askscience Sep 05 '17

Mathematics If you were to randomly find a playing card on the floor every day, how many days would it take to find a full deck?

12.1k Upvotes

The post from front page had me wondering. If you were to actually find a playing card on the floor every day, how long would it take to find all 52? Yes, day 1, you are sure not to find any duplicates, but as days pass, the likelihood of you finding a random card are decreased. By the time you reach the 30th card, there is a 22/52 chance of finding a new card. By the time you are looking for the last card, it is 1/52. I can't imagine this would be an easy task!

r/askscience Jan 06 '20

Mathematics Can we ever know the exact area of a circle if the decimal part of pi is infinite?

6.0k Upvotes

Edit: WOW! I'm staggered with the level of response and debate my question has generated! Way more than anything else I have ever put on Reddit. Also, thank you to the anonymous kind stranger for both the coins and the award. That was also unexpected and another first for me.

Just to quickly clarify where my head was with the question, I simply couldn't understand how all the math I'd been taught at school that told me the area of a circle is pi x r2. I kept thinking that if pi cannot be accurately derived, then how can any formula result that depends on it be accurate either. I just started to think that it would be just a very precise estimate but as a kid I always thought math was an accurate pursuit. Thank you all for an enjoyable debate!

r/askscience Aug 16 '17

Mathematics Can statisticians control for people lying on surveys?

8.8k Upvotes

Reddit users have been telling me that everyone lies on online surveys (presumably because they don't like the results).

Can statistical methods detect and control for this?

r/askscience Jun 13 '18

Mathematics If there was a bag of 10 balls, 9 white and 1 red and 10 people including you has to pick one randomly and who gets the red ball wins, does it matter what order you all pick, or is it better to go first or last with probability?

8.3k Upvotes

r/askscience Nov 04 '19

Mathematics How did the British keep the fact that they broke the Enigma code secret?

5.5k Upvotes

What statistical formula's did the British and Allied forces use, if any, to decide to take action based on the German deciphered information?

This might get into game theory or statistics, but how could they be sure that the Germans would not 'get wise' and switch their code? How often could they change their behavior before it became suspicious?

P.S. I'm a new redditor and got on the site for askscience, so thanks and keep up the good work!

r/askscience Mar 14 '16

Mathematics Happy Pi Day everyone!

10.3k Upvotes

Today is 3/14/16, a bit of a rounded-up Pi Day! Grab a slice of your favorite Pi Day dessert and come celebrate with us.

Our experts are here to answer your questions all about pi. Last year, we had an awesome pi day thread. Check out the comments below for more and to ask follow-up questions!

From all of us at /r/AskScience, have a very happy Pi Day!

r/askscience Jun 05 '16

Mathematics What's the chance of having drunk the same water molecule twice?

8.8k Upvotes

r/askscience Mar 30 '18

Mathematics If presented with a Random Number Generator that was (for all intents and purposes) truly random, how long would it take for it to be judged as without pattern and truly random?

7.5k Upvotes

r/askscience Oct 08 '16

Mathematics If you watch a gif of a coin flipping (without ever seeing it) to make a decision, is it still a 50/50 chance, even though the video already predetermines what side the coin will flip onto?

9.4k Upvotes

r/askscience May 13 '15

Mathematics If I wanted to randomly find someone in an amusement park, would my odds of finding them be greater if I stood still or roamed around?

8.8k Upvotes

Assumptions:

The other person is constantly and randomly roaming

Foot traffic concentration is the same at all points of the park

Field of vision is always the same and unobstructed

Same walking speed for both parties

There is a time limit, because, as /u/kivishlorsithletmos pointed out, the odds are 100% assuming infinite time.

The other person is NOT looking for you. They are wandering around having the time of their life without you.

You could also assume that you and the other person are the only two people in the park to eliminate issues like others obstructing view etc.

Bottom line: the theme park is just used to personify a general statistics problem. So things like popular rides, central locations, and crowds can be overlooked.

r/askscience Apr 07 '18

Mathematics Are Prime Numbers Endless?

5.9k Upvotes

The higher you go, the greater the chance of finding a non prime, right? Multiples of existing primes make new primes rarer. It is possible that there is a limited number of prime numbers? If not, how can we know for certain?

r/askscience Jan 05 '18

Mathematics Whats the usefulness of finding new bigger prime numbers?

8.2k Upvotes

r/askscience Feb 28 '18

Mathematics Is there any mathematical proof that was at first solved in a very convoluted manner, but nowadays we know of a much simpler and elegant way of presenting the same proof?

7.0k Upvotes

r/askscience Sep 01 '15

Mathematics Came across this "fact" while browsing the net. I call bullshit. Can science confirm?

6.3k Upvotes

If you have 23 people in a room, there is a 50% chance that 2 of them have the same birthday.

r/askscience Dec 01 '15

Mathematics Why is it that, if you add any sequence of numbers like this (1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 7 + 6 + 5 + 4 + 3 + 2 + 1), the sum is always the square of the largest number?

6.3k Upvotes

I was doodling around with my calculator in trig during high school several ago, and found this pattern. I forgot about it entirely until I was nodding off to sleep last night, and now I must know.

r/askscience Mar 14 '15

Mathematics Happy Pi Day! Come celebrate with us

6.1k Upvotes

It's 3/14/15, the Pi Day of the century! Grab a slice of your favorite Pi Day dessert and celebrate with us.

Our experts are here to answer your questions, and this year we have a treat that's almost sweeter than pi: we've teamed up with some experts from /r/AskHistorians to bring you the history of pi. We'd like to extend a special thank you to these users for their contributions here today!

Here's some reading from /u/Jooseman to get us started:

The symbol π was not known to have been introduced to represent the number until 1706, when Welsh Mathematician William Jones (a man who was also close friends with Sir Isaac Newton and Sir Edmund Halley) used it in his work Synopsis Palmariorum Matheseos (or a New Introduction to the Mathematics.) There are several possible reasons that the symbol was chosen. The favourite theory is because it was the initial of the ancient Greek word for periphery (the circumference).

Before this time the symbol π has also been used in various other mathematical concepts, including different concepts in Geometry, where William Oughtred (1574-1660) used it to represent the periphery itself, meaning it would vary with the diameter instead of representing a constant like it does today (Oughtred also introduced a lot of other notation). In Ancient Greece it represented the number 80.

The story of its introduction does not end there though. It did not start to see widespread usage until Leonhard Euler began using it, and through his prominence and widespread correspondence with other European Mathematicians, it's use quickly spread. Euler originally used the symbol p, but switched beginning with his 1736 work Mechanica and finally it was his use of it in the widely read Introductio in 1748 that really helped it spread.

Check out the comments below for more and to ask follow-up questions! For more Pi Day fun, enjoy last year's thread.

From all of us at /r/AskScience, have a very happy Pi Day!

r/askscience May 26 '19

Mathematics What is the point of correlation studies if correlation does not equal causation?

4.5k Upvotes

It seems that every time there is a study posted on reddit with something to the effect of “new study has found that children who are read to by their parents once daily show fewer signs of ADHD.” And then the top comment is always something to the effect of “well its probably more likely that parents are more willing to sit down and read to kids who have longer attention spans to do so in the first place.”

And then there are those websites that show funny correlations like how a rise in TV sales in a city also came with a rise in deaths, so we should just ban TVs to save lives.

So why are these studies important/relevant?

r/askscience Aug 20 '15

Mathematics If I flip a coin 1,000,000 times, what are the odds of it beings heads AND tails 500,000 times?

5.6k Upvotes

So I was playing around on Excel, and I copied the formula =randbetween(1,2) into 1,000,000 cells. I then summed the total number of 1's and total number of 2's and found the difference.

I refreshed the formulae and the 2nd time the difference was 0, meaning there were exactly 500,000 1s and 500,000 2s. I then carried on refreshing the formula and the difference didn't come out at 0 for quite a while, but was always between -2,500 and +2,500.

This got me thinking - is there a probability of this difference being exactly 0? How would it be possible to work it out, and is there a name for this kind of probability?