While volunteering at my neighborhood elementary school this morning, a student showed us a subtraction method for problems where the minuend (top number) has one or more zeroes. I had never seen this before. It uses the fact that 50 - 1 = 49, 300 - 1 = 299, 1000 - 1 = 999 etc. She had us put a 'ring' around the relevant part of the minuend and then subtract. See the attached sample.