Mathematics
Grade 8
15 min
Write variable equations: word problems
Write variable equations: word problems
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1
Introduction & Learning Objectives
Learning Objectives
Identify unknown quantities in word problems and represent them with variables.
Translate common English phrases into their corresponding mathematical operations (+, -, *, /).
Distinguish between algebraic expressions and equations within word problems.
Formulate one-variable linear equations from real-world scenarios.
Recognize keywords that indicate equality in word problems.
Check the reasonableness of a formulated equation against the problem context.
Ever wonder how mathematicians solve real-life puzzles like calculating costs or distances? 🗺️ It all starts with turning words into math!
In this lesson, you'll learn the essential skill of translating everyday language into mathematical equations using variables. This skill is fundamental for sol...
2
Key Concepts & Vocabulary
TermDefinitionExample
VariableA symbol, usually a letter (like x, y, or a), used to represent an unknown quantity or a quantity that can change.In the phrase 'Let 'x' be the number of apples,' 'x' is the variable representing the unknown number of apples.
ExpressionA mathematical phrase that contains numbers, variables, and operation symbols (like +, -, *, /), but does NOT contain an equality sign (=).The cost of 3 books at 'b' dollars each, plus a $5 magazine, can be written as the expression `3b + 5`.
EquationA mathematical statement that shows two expressions are equal, connected by an equality sign (=). It asserts that the value on one side is the same as the value on the other side.If the total bill was $41, the expression `3b + 5` becomes the...
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Core Formulas
The 'Translate Keywords' Rule
Identify keywords in the word problem and translate them into their corresponding mathematical operations or symbols.
This rule helps break down the language of the problem into mathematical components. For example: 'sum' means +, 'difference' means -, 'product' means *, 'quotient' means /, and 'is' or 'total' means =.
The 'Define Your Variable' Rule
Clearly state what your variable represents before writing the equation. For example, 'Let `x` be the number of hours worked.'
This rule ensures clarity and helps prevent errors by explicitly linking the variable to the unknown quantity in the problem. It's crucial for understanding what your final answer...
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Challenging
The width of a rectangular garden is 7 feet less than twice its length. If the perimeter is 118 feet, which equation can be used to find the length, `L`?
A.L + (2L - 7) = 118
B.2L + 2(2L) = 118 - 7
C.L(2L - 7) = 118
D.2L + 2(2L - 7) = 118
Challenging
Two siblings, Anna and Ben, share a prize of $500. Anna receives $50 less than one-third of the amount Ben receives. If `b` represents the amount Ben receives, which equation correctly models this situation?
A.(b/3 - 50) + b = 500
B.a + (a/3 - 50) = 500
C.b/3 - 50 = 500
D.b - 50 + b/3 = 500
Challenging
Car Rental Company A charges $30 per day plus $0.25 per mile. Company B charges $50 per day plus $0.15 per mile. Which equation would you use to find the number of miles, `m`, at which the cost for one day of renting from either company is the same?
A.30.25m = 50.15m
B.30 + 0.25m = 50 + 0.15m
C.(30 + 0.25)m = (50 + 0.15)m
D.30 + 50 = 0.25m + 0.15m
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