There are **73** NRICH Mathematical resources connected to **Addition & subtraction**, you may find related items under Calculations and Numerical Methods.

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How many ways can you find to put in operation signs (+ - x Ã·) to make 100?

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Try out some calculations. Are you surprised by the results?

This article suggests some ways of making sense of calculations involving positive and negative numbers.

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There are nasty versions of this dice game but we'll start with the nice ones...

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Here is a chance to play a fractions version of the classic Countdown Game.

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Here is a chance to play a version of the classic Countdown Game.

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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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Different combinations of the weights available allow you to make different totals. Which totals can you make?

How can we help students make sense of addition and subtraction of negative numbers?

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Do you notice anything about the solutions when you add and/or subtract consecutive negative numbers?

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In this game the winner is the first to complete a row of three. Are some squares easier to land on than others?

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Use the differences to find the solution to this Sudoku.

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Delight your friends with this cunning trick! Can you explain how it works?

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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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Can you arrange these numbers into 7 subsets, each of three numbers, so that when the numbers in each are added together, they make seven consecutive numbers?

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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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A cinema has 100 seats. Show how it is possible to sell exactly 100 tickets and take exactly Â£100 if the prices are Â£10 for adults, 50p for pensioners and 10p for children.

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We start with one yellow cube and build around it to make a 3x3x3 cube with red cubes. Then we build around that red cube with blue cubes and so on. How many cubes of each colour have we used?

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Can you find six numbers to go in the Daisy from which you can make all the numbers from 1 to a number bigger than 25?

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How many solutions can you find to this sum? Each of the different letters stands for a different number.

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15 = 7 + 8 and 10 = 1 + 2 + 3 + 4. Can you say which numbers can be expressed as the sum of two or more consecutive integers?

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Three children are going to buy some plants for their birthdays. They will plant them within circular paths. How could they do this?

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An investigation involving adding and subtracting sets of consecutive numbers. Lots to find out, lots to explore.

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Investigate the different ways that fifteen schools could have given money in a charity fundraiser.

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What happens when you add a three digit number to its reverse?

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By selecting digits for an addition grid, what targets can you make?

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Got It game for an adult and child. How can you play so that you know you will always win?

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Some Games That May Be Nice or Nasty for an adult and child. Use your knowledge of place value to beat your opponent.

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Play this game to learn about adding and subtracting positive and negative numbers

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Charlie has made a Magic V. Can you use his example to make some more? And how about Magic Ls, Ns and Ws?

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This challenging activity involves finding different ways to distribute fifteen items among four sets, when the sets must include three, four, five and six items.

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This challenge extends the Plants investigation so now four or more children are involved.

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Fancy a game of cricket? Here is a mathematical version you can play indoors without breaking any windows.

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Skippy and Anna are locked in a room in a large castle. The key to that room, and all the other rooms, is a number. The numbers are locked away in a problem. Can you help them to get out?

This article for teachers suggests ideas for activities built around 10 and 2010.

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This Sudoku, based on differences. Using the one clue number can you find the solution?

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This Sudoku requires you to do some working backwards before working forwards.

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Special clue numbers related to the difference between numbers in two adjacent cells and values of the stars in the "constellation" make this a doubly interesting problem.

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Make your own double-sided magic square. But can you complete both sides once you've made the pieces?

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If you take a three by three square on a 1-10 addition square and multiply the diagonally opposite numbers together, what is the difference between these products. Why?

Find out about Magic Squares in this article written for students. Why are they magic?!

This article gives you a few ideas for understanding the Got It! game and how you might find a winning strategy.

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Is it possible to rearrange the numbers 1,2......12 around a clock face in such a way that every two numbers in adjacent positions differ by any of 3, 4 or 5 hours?

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You have four jugs of 9, 7, 4 and 2 litres capacity. The 9 litre jug is full of wine, the others are empty. Can you divide the wine into three equal quantities?

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Can you arrange the digits 1,2,3,4,5,6,7,8,9 into three 3-digit numbers such that their total is close to 1500?

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The country Sixtania prints postage stamps with only three values 6 lucres, 10 lucres and 15 lucres (where the currency is in lucres).Which values cannot be made up with combinations of these postage. . . .