I light 40 lamps on days that don't end in Y, so how many do I light all week?
I can think of two possible answers. The obvious one where the answer is you don't light any because there are no days that don't end in Y. Or the not so obvious where it's a trick question not referring to the NAMES of the days but just the days themselves, in which case you would light 280 lamps(7*40=280) all week. If I had to put my money on one of these though I'd probably say the first one just based on my past experience with similar riddles.