Riddle #410

Question: When is 1500 plus 20 and 1600 minus 40 the same thing?

Question: What tastes better than it smells?

Question: What loses its head in the morning and gets it back at night?

Question: What two things can you never eat for breakfast?

Question: What asks but never answers?

Question: People see through me, but none pass through without killing me. I can be anywhere, and can be seen double or single. What am I?