Plus Blog
January 21, 2011
<
Negative numbers are easy to imagine if you think of the number line as a giant thermometer which includes subzero temperatures. This makes addition and subtraction easy, as you just move up or down the number line by the according amount. But what about those tricky multiplication rules? Why does positive times negative give negative, and negative times negative give positive? Here the number line can help us too. Suppose you're standing at the point 0, facing in the positive direction of the number line. You take two steps backwards and you do this 4 times. You end up at the point 8, showing that 2 steps times 4 is 8, ie (2)x4=8. Now suppose you're back at 0, this time facing in the negative direction. You take 2 steps forwards and you do this 4 times. You also end up at point 8, showing that 2 steps times 4 is 8, ie 2x(4)=8. Again, go back to 0, looking in the negative direction. Take 2 steps backwards and do this 4 times. You end up at the point 8. Stepping backwards gives you a 2. Facing in the negative direction gives you a 4. Putting all this together gives (2)x(4)=8.
3 comments

January 21, 2011
Straight Statistics is a campaign set up by journalists and statisticians to improve the use of statistics by government, the media, companies and everyone else who uses stats. On the Straight Statistics website you can find all sorts of interesting articles responding to stats as they come up in the news — whether it's lucky house numbers, the impact of bird flu, or your chance to reach your 100th birthday. Have a look at www.straightstatistics.org/. 
January 14, 2011
Sixteenyearold Rebecca Simpson, of Dame Alice Owens School in Potters Bar, has won a national competition to produce a creative photo connected to maths. Winning entry by Rebecca Simpson. The competition was run by Maths Inspiration, a great initiative that runs lecture events in theatres around the country, featuring speakers such as the writer and TV broadcaster Simon Singh. The competition, sponsored by Hewlett Packard, was open to all the 6,000 who attended the shows last autumn. Rebecca's entry, entitled Box and whiskers, depicts a cat being measured for its level of cuteness. It's a play on box and whiskers diagrams, which will be familiar to any GCSE maths pupil. Rob Eastaway, the director of Maths Inspiration (and Plus author), said: "Our shows aim to prove there's more to maths than just taking exams, and humour is an important part of how we present maths. Rebecca's entry really caught the spirit of what we are trying to achieve". Rebecca wins £200 and a signed copy of the book Fermat's Last Theorem by Simon Singh, while her school receives two topofthe range Hewlett Packard graphing calculators. Rob Eastaway has written several articles for Plus: We've also reviewed some of his prolific book output: 
December 20, 2010
This is it! The holidays have started, the turkey is defrosting and the presents are all wrapped ... all you have to do now is relax and be kind to one another. And since Christmas is all about love, the very last door of our advent calendar is devoted to it, too. The Plus team wish you a very merry Christmas and a happy new year! Kissing the frog: a mathematician's guide to mating Baby robots feel the love Love's a gamble Maths on a plane It may seem a bit unromantic, but when it comes down to it, dating is all about strategy. Find out what happens if, like in the film The beautiful mind, everyone goes for the blonde, and if it's possible to be too attractive. 
December 20, 2010
23 is a prime number. Mathematicians love primes. But why? Find out with this prime collection of prime articles. Mathematical mysteries: the Goldbach conjecture Elusive twins Primes lie at the heart of one of the hardest open problems in maths. Find out more with The prime number lottery, The music of the primes and A whirlpool of numbers. Safety in numbers The prime numbers are the atoms amongst the integers, and while we know that there are infinitely many of them, there's no general formula that generates them all. Here are two ways of sieving out all primes up to a given number: Sundaram's sieve and a geometrical method. 
December 20, 2010
Oh, Christmas is so magical! But of course magic often boils down to being surprised. Find out how mathemagicians trade off the fact that you can usually predict precisely the outcome of doing something in mathematics, but only if you know the secret beforehand. Here's for some maths and magic! 