Mathematics Grade 9 15 min

Balance subtraction equations - up to two digits

Balance subtraction equations - up to two digits

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Introduction & Learning Objectives

Learning Objectives Translate word problems involving subtraction into linear equations and inequalities. Apply the Subtraction Property of Equality to isolate variables in multi-step linear equations. Apply the Subtraction Property of Inequality to isolate variables in multi-step linear inequalities. Solve linear equations and inequalities that involve the subtraction of binomial expressions. Represent the solution set of a linear inequality on a number line. Verify solutions to linear equations and inequalities by substitution. Distinguish between the single-value solution of a linear equation and the solution set of a linear inequality. Imagine you have a $95 gift card and want to buy a game, but you also have to pay for a subscription. How do you figure out the maximum...
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Key Concepts & Vocabulary

TermDefinitionExample Linear EquationA mathematical statement asserting that two expressions are equal, forming a straight line when graphed. It has one or more variables, and the highest power of the variable is 1.90 - 5x = 25 Linear InequalityA mathematical statement that compares two expressions using an inequality symbol (<, >, ≤, ≥). The solution is a range of values, not a single number.75 - (2x + 10) > 30 Isolating the VariableThe process of performing inverse operations to get a variable by itself on one side of the equation or inequality.To isolate x in x + 15 = 40, we subtract 15 from both sides. Inverse OperationsOperations that 'undo' each other. Subtraction is the inverse operation of addition.To undo the subtraction of 20 in the expression y - 20, you woul...
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Core Formulas

Subtraction Property of Equality If \(a = b\), then \(a - c = b - c\) You can subtract the same number, variable, or expression from both sides of an equation, and the equation will remain balanced. Subtraction Property of Inequality If \(a > b\), then \(a - c > b - c\). This also applies to \(<, \le, \ge\). You can subtract the same number, variable, or expression from both sides of an inequality without changing the direction of the inequality symbol. Distributing a Negative \(-(a + b) = -a - b\) and \(-(a - b) = -a + b\) When subtracting an expression in parentheses, you must distribute the negative sign to every term inside the parentheses, effectively changing the sign of each term.

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Sample Practice Questions

Challenging
Consider the equation 50 - (2x + 10) = 20 and the inequality 50 - (2x + 10) > 20. How does the solution of the equation relate to the solution set of the inequality?
A.The equation's solution, x=10, is the maximum value in the inequality's solution set.
B.The equation's solution, x=10, is the minimum value in the inequality's solution set.
C.The equation's solution, x=10, serves as the boundary for the inequality's solution set, x < 10.
D.The equation's solution, x=15, is unrelated to the inequality's solution set.
Challenging
A company has a budget of $90. It spends $15 on fixed costs. It also must pay a debt of $8. The remaining money is used to buy raw materials at $4 per unit. To remain profitable, the final amount of money left must be greater than the debt paid. How many full units of raw materials can be purchased?
A.17
B.14
C.15
D.16
Challenging
A student solved 75 - (5 - 2x) < 40 as follows: Step 1: 75 - 5 + 2x < 40 Step 2: 70 + 2x < 40 Step 3: 2x < -30 Step 4: x < -15 In which step did the student make the first mistake, and what was it?
A.Step 3; The student incorrectly applied the Subtraction Property of Inequality.
B.Step 1; The student made a sign error distributing the negative.
C.Step 2; The student incorrectly combined like terms.
D.Step 4; The student should have flipped the inequality symbol.

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