Mental calculations

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Clever Carl

What would you do if your teacher asked you add all the numbers from 1 to 100? Find out how Carl Gauss responded when he was asked to do just that.
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Integrated sums Sudoku

The puzzle can be solved with the help of small clue-numbers which are either placed on the border lines between selected pairs of neighbouring squares of the grid or placed after slash marks on the intersections between two diagonally adjacent squares.
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Let's get flexible!

In this article for primary teachers, Ems outlines how we can encourage learners to be flexible in their approach to calculation, and why this is crucial.
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Transformations tables

Age

7 to 11

Challenge level

These grids are filled according to some rules - can you complete them?
problem
Mind reading

Age

11 to 14

Challenge level

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 know?
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Street lamps

Age

11 to 14

Challenge level

Walking up a steep hill, I pass 10 equally spaced street lamps. How long do I take to walk from the first lamp to the last?
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Intersection sums Sudoku

Age

7 to 16

Challenge level

A Sudoku with clues given as sums of entries.
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Prime magic

Age

7 to 16

Challenge level

Place the numbers 1, 2, 3,..., 9 one on each square of a 3 by 3 grid so that all the rows and columns add up to a prime number. How many different solutions can you find?
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Is it magic or is it maths?

Age

11 to 14

Challenge level

Here are three 'tricks' to amaze your friends. But the really clever trick is explaining to them why these 'tricks' are maths not magic. Like all good magicians, you should practice by trying them. Can you explain how they work?
problem
Two dice

Age

5 to 7

Challenge level

Find all the numbers that can be made by adding the dots on two dice.