Question 2
Opening a numbered door cancels two numbers: the number on that door and the number on the door it covers (the neighbour on the side where its hinges are; for example opening the first door cancels the 2 and the 6 below it). In compensation, a number half the value of the opened door appears behind it. Open four doors so that all four rows and all four columns add up to the same total. Which doors do you open?
