Can a number be both odd and even?
What does this tell you about where the ODD NUMBER and EVEN NUMBER
headings have to go?
Can you use this idea to position any of the other heading
cards?
If you have reached a stage where you have placed most of the
numbers but have a few that you cannot place, don't panic!
Could you swap one of the numbers that you can't place for a number
that is already on the grid?
You might be able to swap them and then find that the number you
have removed can be placed on one of the empty squares.
Don't forget: $1$ is not a prime number!
Triangle
numbers can be represented by a triangular array of
squares
Make a set of numbers that use all the digits from 1 to 9, once and
once only. Add them up. The result is divisible by 9. Add each of
the digits in the new number. What is their sum? Now try some other
possibilities for yourself!