As part of my Christmas gifts from MC I got a puzzle-a-day desk calendar. So far the puzzles have been too easy. Today, however, came a bit of a challenge. Its the sort of thing that is small enough to get by trial and error but I wondered if there was some logical way that you could come to an answer. I don't much fancy the simultaneous equations method but that would surely work too. I'll paraphrase it here: There are 16 rooms in a 4x4 grid, a spy has placed 3 bugs in 2 of the rooms, 2 bugs in 2 of the rooms and 1 bug in 4 other rooms (8 are empty). The number of bugs in each row, column and the one diagonal are as shown in this image: Answers on a postcard please.