Label this plum tree graph to make it totally magic!
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
The diagram illustrates the formula: 1 + 3 + 5 + ... + (2n - 1) = n² Use the diagram to show that any odd number is the difference of two squares.
The 2-digit number is either $65$ or $56$.
Any 2-digit number can be represented as $10a + b$. We need
$(10a+b)^2 - (10b+a)^2 = 99a^2 - 99b^2 =9 \times 11 \times (a^2 -
b^2)$ to be a square.
This means that $(a^2 - b^2)$ must be 11 and so $(a - b)(a + b)
= 11$ making, $a - b = 1$ and $a + b = 11$. This gives $a = 6$, and
$b = 5$.
If we find a solution with $a > b$ then, by reversing the
digits, we get a second solution.