Basic Math & Pre-Algebra All-in-One For Dummies (+ Chapter Quizzes Online). Mark Zegarelli
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time by multiplying 3 times 9, which gives you 27. Therefore, you need 27 hot dogs (plus a whole lot of mustard and sauerkraut).
When you’re first introduced to multiplication, you use the times sign (×). As you move onward and upward on your math journey, you need to be aware of the conventions I discuss in the following sections.
In Units 1 through 4 of this book, I stick to the tried-and-true symbol × for multiplication. Just be aware that the symbol · exists so that you won’t be stumped if your teacher or textbook uses it.
This switch makes sense when you stop to consider that the letter x, which is often used in algebra, looks a lot like the multiplication sign ×. So in this book, when I start using x to discuss algebra topics in Unit 7, I also stop using × and begin using parentheses without another sign to indicate multiplication.
Doing math lickety-split: Division
The last of the Big Four operations is division. Division literally means splitting things up. For example, suppose you’re a parent on a picnic with your three children. You’ve brought along 12 pretzel sticks as snacks, and want to split them fairly so that each child gets the same number (don’t want to cause a fight, right?).
Each child gets four pretzel sticks. This problem tells you that
As with multiplication, division also has more than one sign: the division sign (÷) and the fraction slash (/) or fraction bar (—). So, some other ways to write the same information are
Whichever way you write it, the idea is the same: When you divide 12 pretzel sticks equally among three people, each person gets 4 of them.
Applying the Big Four Operations to Larger Numbers
So, be honest. Are you’re feeling a bit shaky about how to apply the Big Four operations to larger numbers, especially long division? If so, don’t worry. Just use this section as a handy reference for remembering how to do stacked addition, subtraction, and multiplication, as well as everybody’s favorite, long division.
Calculating stacked addition
Stacked addition allows you to add large numbers in a systematic way.
For example, to add
Next, starting in the ones’ column and working from right to left, add the numbers and place each result below the line:
Thus,
In most cases when you add, the calculation will involve carrying at least one digit from one column to the next.
For example, suppose you want to add
Next, add
To complete the problem, add
Therefore,
Performing stacked subtraction
As with addition, stacked subtraction allows you to subtract larger numbers systematically.
For example, to subtract
Now, as with addition, start in the ones’ column and work right to left, this time subtracting each pair of numbers in the column, and place each result below the line:
So
In most cases when you subtract, the calculation will involve borrowing at least one digit from one column to the next.
For example, suppose you want to subtract
To begin, you want to subtract
Now,