When solving problems it is sometimes necessary to translate words, a table of data, or a physical model into expressions. There are two types of expressions: variable and numerical. Variable expressions have at least one variable (sometimes called an unknown) in them. Numerical expressions involve only numbers. Here are examples of each
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Here is a table of key words that indicate addition and subtraction.
Operation |
Verbal expressions (key words) |
Variable expression |
$\large~+$ |
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$\large~n+3$ |
$\large~-$ |
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$\large~x-12$ |
Example 1
To find Bill's age, begin by placing their ages in a table...
When Angela's age is... | Bill's age is... |
5 | 8 |
6 | 9 |
7 | 10 |
12 | |
n | n+3 |
Notice that Bill is always 3 years older than Angela. So when Angela is 12 years old Bill will be 15 years old.
When Angela is n years old, Bill will be (n+3) years old.
Example 2
Alan is 8 years old.
Example 3
EXPLORE!
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Question 1 Two sticks are laid end-to-end. Their combined length is 18 inches. The shorter stick is m inches long. What is the length of the longer stick? |
[show answer] |
Question 2 Let a, b, and c represent the three lengths of the three sides of a triangle. What is the perimeter of the triangle? |
[show answer] |
Question 3 If the initial temperature is d degrees how many degrees will it be if the temperature goes up 3 degrees? |
[show answer] |