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Variables as Unknown Numbers
Overview
Variables can represent unknown numbers. We can use what we know about mathematical operations to determine the value of these unknown numbers. For example…
Determine the value of x in the expression
5x = 35
We can read the expression as 5 times what number equals 35?
We can use the relationship between multiplication and division to solve for x
5x = 35
Divide both sides by 5 to get x by itself.
We can check our answer by plugging the value back into the original equation.
5 (7) = 35 ✔
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Determine the value of x in the expression x – 3 = 1
Answer
4
1 + 3 = 4
Determine the value of x in the expression 6x = 60
Answer
10
Determine the value of x in the expression 2x + 3 = 9
Answer
3
Determine the value of x in the expression x ÷ 16 = 2
Answer
32
x = 2(16)
Sarah had 15 pencils when she went to school this morning. She gave x number of pencils away. Now she has 3 pencils left. Write an equation to represent the number of pencils she gave away. Then solve for x.
Answer
15 – x = 3; x = 12
15 – 3 = 12
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