Author Topic: A collection of cool mathematical facts  (Read 23 times)

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Offline Mave

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A collection of cool mathematical facts
« on: June 22, 2017, 05:17 »
if you fold a piece of paper 103 times, the thickness of it will be larger than the observable universe.  (which is 93 billion light-years)



The optimal number of moves needed to solve a Rubik's cube from any configuration is only 20.



If you have 23 people in a room, there is a 50% chance that at least two of them have the same birthday. If you put 70 people in, the probability jumps to 99.9%.



1 x 1 = 1

11 x 11 = 121

111 x 111 = 12321

1111 x 1111 = 1234321

etc.



No matter how often you multiply 90625 with itself, it will always have 90625 at the end.

90625

90625² = 8212890625

90625³ = 744293212890625

etc.



Suppose a drug test is 99% sensitive and 99% specific. That is, the test will produce 99% true positive results for drug users and 99% true negative results for non-drug users. Suppose that 0.5% of people are users of the drug. If a randomly selected individual tests positive, what is the probability that he is a user?

The answer is around 33.2%



Source: Reddit

Offline Stybar

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Re: A collection of cool mathematical facts
« Reply #1 on: June 22, 2017, 03:42 »