I just came across a maths puzzle,where i should get the sum of 9 numbers(multiples of 10) to be 450 both horizontally and vertically in a 9x9 matrix.
Picture attached for reference:
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There are actually lots of solution to this problem. Here is an example:
I did remove $10$ times from the table to show it more clear. But if you ask me how I solved it;
I just put numbers from 9 to 1 in the matrix one by one, for example I have started putting the number from 9 as below:
The location chosen according to the idea of the puzzle, yellow area shows where you cannot put the 9s. the green area is the safe places where you can put 9s but they should not be on the same row and column as shown in the graph above.
The rest is just trial and error with the same methodology explained here.