Idiot\'s Guides Basic Math and Pre-Algebra

CHAPTER

2 Arithmetic

In This Chapter

• Practice addition with
  regrouping


• Learn to look for compat-
  ible numbers


• Practice subtraction with
  regrouping


• Make change for mental
  subtraction


• Practice multiplication of
  multi-digit numbers


• Practice the long division
  algorithm

The last chapter focused on the world of numbers and how to

express those numbers in words and symbols. The next step is

investigating how to work with numbers. In other words, it’s

time to look at arithmetic.

The two fundamental operations of arithmetic are addition

and multiplication (and multiplication is actually a shortcut

for repeated addition). Subtraction and division are usually

included in the basics of arithmetic, but you’ll see that these

are really operations that reverse on addition and multipli-

cation. We’ll look at the basics of skillful arithmetic and

introduce some strategies that may make the work easier.

Addition and Subtraction .......................................................................................................

The counting numbers came to be because people needed to

count. Soon thereafter, people started putting together and

taking apart the things, or groups of things, they had counted.

If you have 3 fish and your best buddy has 5 fish, you have a

pretty satisfying meal (unless you invite 20 friends, but that’s

division and that’s later). You could put all the fish in a pile

and count them again, but soon you get the notion of 3 + 5

= 8. And if you only eat 4 fish, again, you could count the