http://plus.maths.org/content/Blog/2009/12/www.britishscienceassociation.org/forms/latestnews/%20http%3A/http%3A/issue16/features/derivatives/index.html en Plus Advent Calendar Door #13: Simpson's paradox http://plus.maths.org/content/plus-advent-calendar-door-13-simpsons-paradox <p>No, this isn't about Homer, but it's interesting anyway. Suppose you're trying to decide which university to go to. You find out that last year the university you're interested in admitted 30% of male applicants but only 21.3% of female applicants. Looks like a clear case of gender bias, so you're tempted to go somewhere else. But then you look at the figures again, this time broken up by department. The university only has two departments, maths and English. The English department admitted 40% of male applicants and 42% of female applicants.<p><a href="http://plus.maths.org/content/plus-advent-calendar-door-13-simpsons-paradox" target="_blank">read more</a></p> http://plus.maths.org/content/plus-advent-calendar-door-13-simpsons-paradox#comments Advent calendar 2013 Fri, 13 Dec 2013 11:09:42 +0000 mf344 5997 at http://plus.maths.org/content Plus Advent Calendar Door #12: 1, 2, 3, ... http://plus.maths.org/content/plus-advent-calendar-door-12-1-2-3 <p>There's nothing simpler than 1,2,3, ... we understand these numbers instinctively and that's why they're called the natural numbers. But if you really think about it, what are these numbers? How would you describe them to an alien devoid of a number instinct? Here's one way of defining them, developed by the Italian mathematician <a href="http://www-history.mcs.st-and.ac.uk/Biographies/Peano.html">Giuseppe Peano</a>:</p><p><a href="http://plus.maths.org/content/plus-advent-calendar-door-12-1-2-3" target="_blank">read more</a></p> http://plus.maths.org/content/plus-advent-calendar-door-12-1-2-3#comments Advent calendar 2013 Thu, 12 Dec 2013 10:45:43 +0000 mf344 5996 at http://plus.maths.org/content Plus Advent Calendar Door #11: Cross Hyperlogikion! http://plus.maths.org/content/plus-advent-calendar-door-11-cross-hyperlogikion <p>Lately we've been featuring a range of Sudoku-esque puzzles kindly provided by <em>Muddled Puzzles</em>. The puzzles owe their origin to Sudoku and go by the umbrella brand name <a href="http://mindnumbers.com/">Sudokion</a>. Here is our latest addition: the Cross HyperLogikion. It's a challenging and beautiful specialty puzzle, only available in the Platinum (highest) challenge band. For more (and also less challenging) Sudokion puzzles, see our <a href="http://plus.maths.org/content/sudokion-0">Sudokion page</a>.</p> <p>To see the rules of Cross HyperLogikion click on the "i" icon below. </p><p><a href="http://plus.maths.org/content/plus-advent-calendar-door-11-cross-hyperlogikion" target="_blank">read more</a></p> http://plus.maths.org/content/plus-advent-calendar-door-11-cross-hyperlogikion#comments Advent calendar 2013 Wed, 11 Dec 2013 10:17:05 +0000 mf344 5995 at http://plus.maths.org/content Plus Advent Calendar Door #10: Positional genius http://plus.maths.org/content/plus-advent-calendar-door-10-positional-genius <div class="rightimage"><img src="/sites/plus.maths.org/files/articles/2012/counting/ten.jpg" width="300" height="299" alt="ten"/></div> <p> If it wasn't for the Babylonians who lived millennia ago, paying your bill at a restaurant or checking your credit card bill would be much more painful than it already is. And so would anything else involving numbers.<p><a href="http://plus.maths.org/content/plus-advent-calendar-door-10-positional-genius" target="_blank">read more</a></p> http://plus.maths.org/content/plus-advent-calendar-door-10-positional-genius#comments Advent calendar 2013 Tue, 10 Dec 2013 08:33:32 +0000 Rachel 5994 at http://plus.maths.org/content Plus Advent Calendar Door #9: The missing pound http://plus.maths.org/content/plus-advent-calendar-door-9-missing-pound <p> I went Christmas shopping yesterday, to buy a book from the local bookshop that costs £7. I didn't have any money, so I borrowed £5 from Marianne and £5 from Owen. I bought the book and got £3 change. I gave £1 back to each of my kind colleagues and I keep the remaining £1. I now owe each of them £4 and I have £1, giving £9 in total. But I borrowed £10. Where's the missing pound? </p> <div class="centreimage"><img src="/issue24/features/budd/freeimagesmoney.jpg" width="400" height="300" alt="pund coins"/><p>There it is!</p><p><a href="http://plus.maths.org/content/plus-advent-calendar-door-9-missing-pound" target="_blank">read more</a></p> http://plus.maths.org/content/plus-advent-calendar-door-9-missing-pound#comments Advent calendar 2013 Mon, 09 Dec 2013 08:25:15 +0000 Rachel 5993 at http://plus.maths.org/content Plus Advent Calendar Door #8: Counting infinities http://plus.maths.org/content/plus-advent-calendar-door-8-counting-infinities <p> An infinite set is called countable if you can count it. In other words, it's called countable if you can put its members into one-to-one correspondence with the natural numbers 1, 2, 3, ... . For example, a bag with infinitely many apples would be a countable infinity because (given an infinite amount of time) you can label the apples 1, 2, 3, ... and so on. </p><p><a href="http://plus.maths.org/content/plus-advent-calendar-door-8-counting-infinities" target="_blank">read more</a></p> http://plus.maths.org/content/plus-advent-calendar-door-8-counting-infinities#comments Advent calendar 2013 Sun, 08 Dec 2013 08:10:32 +0000 Rachel 5992 at http://plus.maths.org/content