We often talk of dividing as being the reverse of multiplying, and indeed when dividing fractions this is the case. The way you divide fractions is very similar to the way fractions are multiplied with a simple twist in the middle.
Addition is an operation in which one number is added to another number. When adding a series of numbers, there are some strategies that help simplify the addition process. One thing to remember is to group numbers to make tens. For example, when adding 2 + 7 + 8, you can add the 2 and the eight first to get ten, and then add the seven to get 17. Some teachers call these groups of numbers that add to ten, "friendly tens," since they make adding easier for the student.