Add new comment

Want facts and want them fast? Our Maths in a minute series explores key mathematical concepts in just a few words.
Generating electricity without the use of fossil fuels is not just an engineering and industrial challenge, it is also a huge mathematical challenge.
In this podcast author Coralie Colmez shares insights into her novel The irrational diary of Clara Valentine.
We talk to early career mathematicians who spent some of their summer holiday solving problems posed by industry — such as how to blend a perfect smoothie!
Don't like plantbased meat alternatives, but want to spare animals and the environment? There's hope on the horizon, aided by a good helping of maths.
Inverse problems are mathematical detective problems. They can help solve crimes, are used in medical imaging, and much more.
I viewed Tony Sale's page to try to understand the math behind 150 million million permutations for the plugboard. His math was far too advanced for me, so I tried to approach it from a practical point of view.
With the first cord, I have 26 letters to choose from for one end, then (since a letter can't be plugged into itself) I have 25 letters to choose from for the other end. Since a letter can only be plugged into 1 other letter, that leaves 24 letters to choose from for the next cord.
Factoring 26 X 25 X 24 X ... X 7, my calculator showed the answer of approx. 5.6e23 or 56 thousand million million million, a number that's over 3.6 trillion times greater than the number that is reported in this article.
Is my calculator wrong or did Mr. Sale make a mistake? I genuinely would like to know, because I don't understand it.