Why do this problem?
starts very easily but becomes harder with the second and third matrices. The last part, discovering how to work out how the matrix is made up, is really challenging because there are so few clues.
You could start by doing the first magic matrix on the board together. It is not very surprising when all get the same answer! If anyone gets $11$, for example, instead of $10$, you can check quickly that they are doing it correctly. Then let the class try another couple for themselves, perhaps suggesting that they make sure they choose different numbers from their neighbours. Those
confident with decimals and fractions could try then the next two matrices. This sheet gives six copies of the first matrix and three copies for each of the second and third ones.
After that you could introduce the next matrix with the magic total of $100$, and then continue to show the class how it is built up. For this purpose you can use this sheet with the illustrations from the problem.
After this, the group could be challenged to work in pairs making their own magic matrices. It is advisable to limit these to magic totals between $12$ and $200$. This sheet has six copies of the frame for the matrix. However, squared paper can easily be used
The final challenge, to discover what numbers were used to make any of the original three matrices is hard, and could, perhaps, be reserved for the most able learners.
Why not try one of the other matrices?
How can the same number result whichever choices are made?
What number are you choosing for your own matrix?
How are you going to divide it into eight numbers?
You could start with the numbers in the top row of the matrix.
What two numbers could be added together to make $1$?
When the numbers that were used to make up all three of the original matrices have been found, learners could make a larger matrix such as one on a $5$ by $5$ grid.
Suggest sticking with the first matrix and then trying the one which adds to $100$.