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Find all the ways of placing the numbers 1 to 9 on a W shape, with 3 numbers on each leg, so that each set of 3 numbers has the same total.
2-digit Square
A 2-Digit number is squared. When this 2-digit number is reversed and squared, the difference between the squares is also a square. What is the 2-digit number?
Age 14 to 16 Challenge Level:
Charlie has been designing tablecloths for each weekday. He likes to use as many colours as he possibly can but insists that his tablecloths have some symmetry.
The $5$ by $5$ tablecloths below each satisfy a different symmetry rule.
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Monday's $5$ by $5$ tablecloth has just $1$ line of symmetry.
Design some tablecloths of other sizes with just $1$ line of symmetry.
Can you find a way of working out how many colours would be needed for an n by n tablecloth (where n is odd)?
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Tuesday's $5$ by $5$ tablecloth has rotational symmetry of order $4$, and no lines of symmetry.
Design some tablecloths of other sizes with rotational symmetry of order $4$, and no lines of symmetry.
Can you find a way of working out how many colours would be needed for an n by n tablecloth (where n is odd)?
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Wednesday's $5$ by $5$ tablecloth has $2$ lines of symmetry (horizontal and vertical), and rotational symmetry of order $2$.
Design some tablecloths of other sizes with $2$ lines of symmetry, and rotational symmetry of order $2$.
Can you find a way of working out how many colours would be needed for an n by n tablecloth (where n is odd)?
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Thursday's $5$ by $5$ tablecloth has $2$ (diagonal) lines of symmetry and rotational symmetry of order $2$.
Design some tablecloths of other sizes with $2$ (diagonal) lines of symmetry and rotational symmetry of order $2$.
Can you find a way of working out how many colours would be needed for an n by n tablecloth (where n is odd)?
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Friday's $5$ by $5$ tablecloth has $4$ lines of symmetry and rotational symmetry of order $4$.
Design some tablecloths of other sizes with $4$ lines of symmetry and rotational symmetry of order $4$.
Can you find a way of working out how many colours would be needed for an n by n tablecloth (where n is odd)?
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EXTENSION
At weekends Charlie likes to use tablecloths with an even number of squares. Investigate the number of colours that are needed for different types of symmetric $n$ by $n$ tablecloths where $n$ is even.
NRICH is part of the family of activities in the Millennium Mathematics Project.