A drawer is divided into 9 square boxes, creating a 3*3 grid.
Your task is to create a "magic square" by putting a distinct amount of money in each of the boxes in a way that all of the 8 sums (vertical, horizontal and diagonal) will be the same.
Only standard American coins are allowed, i.e. 1,5,10,25,50, and 100c.
What is the minimal amount of coins ?
Show their distribution.
The problem does not say that we need to put coins in every box.
0 cents is arguably an amount of money.
If we are allowed to put 0 cents in one of the boxes, then
Working left to right, top to bottom
Boxes
5 40 15
30 20 10
25 0 35
containing 1+3+2+2+2+1+1+0+2=14 coins.
This is 3 coins less than other solutions, and I doubt that it can be improved upon.