60http://nrich.maths.org/secondary-upperen 2012 http://nrich.maths.org/public/terms.phphttp://nrich.maths.org/9961Wed, 01 Dec 1999 00:00:01 +0000Complex numbers can be represented graphically using an Argand diagram. This problem explains more...http://nrich.maths.org/9859Fri, 01 Feb 2013 00:00:01 +0000In this problem, we define complex numbers and invite you to explore what happens when you add and multiply them.http://nrich.maths.org/9858Fri, 01 Feb 2013 00:00:01 +0000In this follow-up to the problem Odds and Evens, we invite you to analyse a probability situation in order to find the general solution for a fair game.http://nrich.maths.org/9538Mon, 01 Oct 2012 00:00:01 +0100How can you quickly sort a suit of cards in order from Ace to King?http://nrich.maths.org/8192Mon, 01 Oct 2012 00:00:01 +0100What happens when we square complex numbers? Can the square of a complex number be real?http://nrich.maths.org/8109Fri, 01 Mar 2013 00:00:01 +0000Watch the video to see how to sum the sequence. Can you adapt the method to sum other sequences?http://nrich.maths.org/8054Mon, 01 Oct 2012 00:00:01 +0100Six samples were taken from two distributions but they got muddled up. Can you work out which list is which?http://nrich.maths.org/7731Mon, 01 Aug 2011 00:00:01 +0100Can you decide whether these short statistical statements are always, sometimes or never true?http://nrich.maths.org/7721Mon, 01 Aug 2011 00:00:01 +0100Charlie likes to go for walks around a square park, while Alison likes to cut across diagonally. Can you find relationships between the vectors they walk along?http://nrich.maths.org/7453Tue, 01 Feb 2011 00:00:01 +0000Take three whole numbers. The differences between them give you three new numbers. Find the differences between the new numbers and keep repeating this. What happens?http://nrich.maths.org/7223Tue, 01 Feb 2011 00:00:01 +0000A weekly challenge: these are shorter problems aimed at Post-16 students or enthusiastic younger students.http://nrich.maths.org/7056Tue, 01 Feb 2011 00:00:01 +0000This black box reveals random values of some important, but unusual, mathematical functions. Can you deduce the purpose of the black box?http://nrich.maths.org/7029Tue, 01 Feb 2011 00:00:01 +0000Here is a machine with four coloured lights. Can you make two lights switch on at once? Three lights? All four lights?http://nrich.maths.org/7016Tue, 01 Feb 2011 00:00:01 +0000Explore the meaning of the scalar and vector cross products and see how the two are related.http://nrich.maths.org/6576Tue, 01 Feb 2011 00:00:01 +0000Can you make matrices which will fix one lucky vector and crush another to zero?http://nrich.maths.org/6575Tue, 01 Feb 2011 00:00:01 +0000Starting with two basic vector steps, which destinations can you reach on a vector walk?http://nrich.maths.org/6572Tue, 01 Feb 2011 00:00:01 +0000Can you find the volumes of the mathematical vessels?http://nrich.maths.org/6426Tue, 01 Feb 2011 00:00:01 +0000Match the charts of these functions to the charts of their integrals.http://nrich.maths.org/6412Tue, 01 Feb 2011 00:00:01 +0000Can you work out the means of these distributions using numerical methods?http://nrich.maths.org/6411Wed, 01 Jun 2011 00:00:01 +0100Can you find the area of the central part of this shape? Can you do it in more than one way?http://nrich.maths.org/6328Tue, 01 Feb 2011 00:00:01 +0000Are these statistical statements sometimes, always or never true? Or it is impossible to say?http://nrich.maths.org/6149Tue, 01 Feb 2011 00:00:01 +0000Try to solve this very difficult problem and then study our two suggested solutions. How would you use your knowledge to try to solve variants on the original problem?http://nrich.maths.org/5963Tue, 01 Feb 2011 00:00:01 +0000Use your skill and judgement to match the sets of random data.http://nrich.maths.org/5933Tue, 01 Feb 2011 00:00:01 +0000In 15 years' time my age will be the square of my age 15 years ago. Can you work out my age, and when I had other special birthdays?http://nrich.maths.org/631Tue, 01 Feb 2011 00:00:01 +0000