Teaching Notes 1.7: Writing Expressions
Writing expressions is a prerequisite skill to writing equations. Most of the errors students make
in writing expressions arise from misinterpreting words and phrases, particularly those having to
do with subtraction and division.- Explain that key words often signal addition, subtraction, multiplication, and division.
Following are some examples:- Addition:add, total, in all, combine, sum, increased by
- Subtraction:less than, more than, subtract, difference, decreased by
- Multiplication:product, multiply, of, twice, double, triple
- Division:divide, quotient, split, groups of, quarter
- Direct your students to focus their attention on subtraction and division. Point out that
unlike addition and multiplication, subtraction and division are not commutative; the proper
order of the terms cannot be switched. - Provide the following example: 4 less than a numbern. Ask your students to write an expres-
sion for this phrase, then discuss the answer. Explain that although 4 comes first in the
phrase,itmustbeplacedafterthenin the expression. The correct expression for the phrase
4lessthannisn−4. It cannot be 4−n. Offer this illustration: 6− 4 = 4 −6. - Provide this example: A numberndivided by 2. Ask your students to write an expression for
this phrase. It isn÷2. Note that it cannot be 2÷n. Offer this illustration: 4÷ 2 = 2 ÷4. - Review the chart on the worksheet with your students. You might ask your students to gen-
erate more examples.
EXTRA HELP:
To check your work when writing expressions, pick a number, substitute it for the variable, and
see if the result is reasonable.ANSWER KEY:
(1)n+6or6+n (2)n− 1 (3) 3 n (4)n− 8 (5)n÷ 10 (6)n− 9 (7)n− 6 (8) 3 +norn+ 3
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(Challenge)Answers may vary. An acceptable response is 3 less than twice a number.
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