Mathematics Grade 9 15 min

Subtract a one-digit number from a two-digit number up to 18

Subtract a one-digit number from a two-digit number up to 18

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1

Introduction & Learning Objectives

Learning Objectives Model the subtraction of a one-digit number from a two-digit number (10-18) using a linear algebraic equation. Define a function f(x, y) = x - y and specify the domains for x and y according to the lesson's constraints. Solve for an unknown variable in first-degree equations, such as 17 - x = 9 or y - 5 = 11, and verify the solution against given constraints. Evaluate multi-step algebraic expressions, including polynomials, where variable substitution results in this specific type of subtraction. Translate word problems involving this subtraction scenario into algebraic expressions and solve for the required value. Analyze the set of possible outcomes (the range) given the constrained domains of the variables. What if a simple calculation like 15 - 8...
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Key Concepts & Vocabulary

TermDefinitionExample VariableA symbol, typically a letter, that represents an unknown or changing numerical value.In the equation `16 - x = 7`, the letter `x` is a variable representing the number 9. DomainThe complete set of possible input values (for a variable or function) that are valid within a given context.For subtracting a one-digit number (`y`) from a two-digit number up to 18 (`x`), the domain of `x` is `{10, 11, 12, 13, 14, 15, 16, 17, 18}` and the domain of `y` is `{1, 2, 3, 4, 5, 6, 7, 8, 9}`. ConstraintA condition, limitation, or rule that a variable or set of variables must satisfy.In the problem 'Solve `14 - y = z`', a constraint might be '`y` must be an even, one-digit number', which limits the possible values of `y` to {2, 4, 6, 8}. Linear EquationAn...
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Core Formulas

Solving for a Variable in Subtraction (Subtrahend) If `a - x = b`, then `x = a - b` Use this rule to find the value being subtracted (the subtrahend) when you know the initial amount (minuend) and the result (difference). Solving for a Variable in Subtraction (Minuend) If `x - a = b`, then `x = a + b` Use this rule to find the initial amount (the minuend) when you know the value being subtracted (subtrahend) and the result (difference). Function Definition with Domain Constraints f(x, y) = x - y, where Domain(x) = {n | n \in \mathbb{Z}, 10 \le n \le 18} and Domain(y) = {n | n \in \mathbb{Z}, 1 \le n \le 9} This formally defines the operation as a function of two variables, `x` and `y`, and explicitly states the integer constraints on their possible values using set-b...

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Sample Practice Questions

Challenging
Let f(x, y) = x - y, with Domain(x) = {10,...,18} and Domain(y) = {1,...,9}. If f(x, y) = 9, which of the following pairs (x, y) is a valid solution where x must also be a prime number?
A.(18, 9)
B.(15, 6)
C.(17, 8)
D.(11, 2)
Challenging
Consider the function f(x, y) = x - y with Domain(x) = {10, ..., 18} and Domain(y) = {1, ..., 9}. Let R be the set of all possible outcomes (the range). What is the value of max(R) - min(R)?
A.9
B.16
C.17
D.8
Challenging
A variable k is the larger positive integer solution to the quadratic equation k² - 5k + 4 = 0. What is the value of the expression 15 - k?
A.11
B.14
C.10
D.15

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