Problems should use the Courier font. Why? Every Courier font character uses the same amount of space. A comma is the same width as the number 5. This means that all of the numbers line up perfectly for carrying during addition and bringing the zero down in division.
Whereís the answer sheet? Are the answers correct? Are the answers listed in a column that you have to match with the student worksheets or on a replica of the student page laced with answers? Last thing you need is to be in a hurry and red mark student worksheets...when their answers were correct all along.