There are **166** NRICH Mathematical resources connected to **Creating and manipulating expressions and formulae**, you may find related items under Algebraic expressions, equations and formulae.

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Can you find pairs of differently sized windows that cost the same?

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Can you find a way of counting the spheres in these arrangements?

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Watch these videos to see how Phoebe, Alice and Luke chose to draw 7 squares. How would they draw 100?

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Think of a number and follow my instructions. Tell me your answer, and I'll tell you what you started with! Can you explain how I know?

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Jo made a cube from some smaller cubes, painted some of the faces of the large cube, and then took it apart again. 45 small cubes had no paint on them at all. How many small cubes did Jo use?

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How could Penny, Tom and Matthew work out how many chocolates there are in different sized boxes?

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A country has decided to have just two different coins, 3z and 5z coins. Which totals can be made? Is there a largest total that cannot be made? How do you know?

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Can you make sense of these three proofs of Pythagoras' Theorem?

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Can you find rectangles where the value of the area is the same as the value of the perimeter?

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Crosses can be drawn on number grids of various sizes. What do you notice when you add opposite ends?

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How good are you at finding the formula for a number pattern ?

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There is a particular value of x, and a value of y to go with it, which make all five expressions equal in value, can you find that x, y pair ?

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Manufacturers need to minimise the amount of material used to make their product. What is the best cross-section for a gutter?

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If a sum invested gains 10% each year how long before it has doubled its value?

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If the hypotenuse (base) length is 100cm and if an extra line splits the base into 36cm and 64cm parts, what were the side lengths for the original right-angled triangle?

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Is there a temperature at which Celsius and Fahrenheit readings are the same?

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Jo has three numbers which she adds together in pairs. When she does this she has three different totals: 11, 17 and 22 What are the three numbers Jo had to start with?”

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Can you find the area of a parallelogram defined by two vectors?

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Can you see how to build a harmonic triangle? Can you work out the next two rows?

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Imagine starting with one yellow cube and covering it all over with a single layer of red cubes, and then covering that cube with a layer of blue cubes. How many red and blue cubes would you need?

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We can show that (x + 1)² = x² + 2x + 1 by considering the area of an (x + 1) by (x + 1) square. Show in a similar way that (x + 2)² = x² + 4x + 4

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Pick a square within a multiplication square and add the numbers on each diagonal. What do you notice?

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In this 100 square, look at the green square which contains the numbers 2, 3, 12 and 13. What is the sum of the numbers that are diagonally opposite each other? What do you notice?

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This shape comprises four semi-circles. What is the relationship between the area of the shaded region and the area of the circle on AB as diameter?

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To break down an algebraic fraction into partial fractions in which all the denominators are linear and all the numerators are constants you sometimes need complex numbers.

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Imagine a large cube made from small red cubes being dropped into a pot of yellow paint. How many of the small cubes will have yellow paint on their faces?

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Think of a number and follow the machine's instructions... I know what your number is! Can you explain how I know?

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The sums of the squares of three related numbers is also a perfect square - can you explain why?

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When number pyramids have a sequence on the bottom layer, some interesting patterns emerge...

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Try entering different sets of numbers in the number pyramids. How does the total at the top change?

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Choose four consecutive whole numbers. Multiply the first and last numbers together. Multiply the middle pair together. What do you notice?

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My two digit number is special because adding the sum of its digits to the product of its digits gives me my original number. What could my number be?

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Show that if you add 1 to the product of four consecutive numbers the answer is ALWAYS a perfect square.

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How many more miles must the car travel before the numbers on the milometer and the trip meter contain the same digits in the same order?

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Think of a number, add one, double it, take away 3, add the number you first thought of, add 7, divide by 3 and take away the number you first thought of. You should now be left with 2. How do I. . . .

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A, B & C own a half, a third and a sixth of a coin collection. Each grab some coins, return some, then share equally what they had put back, finishing with their own share. How rich are they?

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Can you prove that twice the sum of two squares always gives the sum of two squares?

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Polygons drawn on square dotty paper have dots on their perimeter (p) and often internal (i) ones as well. Find a relationship between p, i and the area of the polygons.

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Given an equilateral triangle inside an isosceles triangle, can you find a relationship between the angles?

Take a complicated fraction with the product of five quartics top and bottom and reduce this to a whole number. This is a numerical example involving some clever algebra.

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Think of two whole numbers under 10, and follow the steps. I can work out both your numbers very quickly. How?

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Charlie likes tablecloths that use as many colours as possible, but insists that his tablecloths have some symmetry. Can you work out how many colours he needs for different tablecloth designs?

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How many winning lines can you make in a three-dimensional version of noughts and crosses?

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Can you produce convincing arguments that a selection of statements about numbers are true?

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Find the missing angle between the two secants to the circle when the two angles at the centre subtended by the arcs created by the intersections of the secants and the circle are 50 and 120 degrees.

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Many numbers can be expressed as the difference of two perfect squares. What do you notice about the numbers you CANNOT make?

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A mother wants to share a sum of money by giving each of her children in turn a lump sum plus a fraction of the remainder. How can she do this in order to share the money out equally?

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A circle of radius r touches two sides of a right angled triangle, sides x and y, and has its centre on the hypotenuse. Can you prove the formula linking x, y and r?

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Take any two numbers between 0 and 1. Prove that the sum of the numbers is always less than one plus their product?

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Two motorboats travelling up and down a lake at constant speeds leave opposite ends A and B at the same instant, passing each other, for the first time 600 metres from A, and on their return, 400. . . .