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.
Maths worksheets should challenge students and at the same time should not be a scary subject to attempt. Worksheets are a recommended mathematic learning source and an amalgam of the total syllabi. They are the top priority in the education system and are used as a learning tool by many parents, schools, teachers and students.