Mathematics
Grade 7
15 min
Find the number of each type of coin
Find the number of each type of coin
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1
Introduction & Learning Objectives
Learning Objectives
Identify unknown quantities and assign appropriate variables for different coin types.
Formulate linear equations representing the total number of coins in a given scenario.
Construct linear equations representing the total monetary value of coins.
Apply the substitution method to solve systems of two linear equations.
Interpret the solutions in the context of the original coin problem.
Verify the reasonableness and accuracy of solutions by checking against problem conditions.
Ever wondered how many dimes and quarters are in your piggy bank if you know the total number of coins and their total value? 💰 Let's find out!
In this lesson, you'll learn powerful problem-solving strategies to determine the exact number of each type of coin when given...
2
Key Concepts & Vocabulary
TermDefinitionExample
VariableA symbol, usually a letter, that represents an unknown number or quantity.In 'Let 'd' be the number of dimes,' 'd' is the variable.
EquationA mathematical statement that shows two expressions are equal.$d + q = 10$ is an equation stating the number of dimes and quarters totals 10.
Monetary ValueThe worth of a coin or collection of coins in terms of currency.The monetary value of 5 dimes is $5 \times $0.10 = $0.50.
System of EquationsA set of two or more equations that share common variables and are solved simultaneously.$d + q = 10$ and $0.10d + 0.25q = 1.90$ form a system of equations.
Substitution MethodAn algebraic technique used to solve systems of equations by solving one equation for one variable and substituting that expre...
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Core Formulas
Total Number of Items Equation
$N = x_1 + x_2 + ... + x_k$
Use this rule to create an equation when the total count of different types of items (like coins) is given. Here, $N$ is the total number of items, and $x_i$ represents the number of items of each specific type.
Total Monetary Value Equation
$V = v_1 x_1 + v_2 x_2 + ... + v_k x_k$
Use this rule to create an equation when the total monetary value of different types of coins is given. Here, $V$ is the total value, $v_i$ is the value of a single coin of type $i$, and $x_i$ is the number of coins of type $i$. (Ensure consistent units, e.g., all in cents or all in dollars).
Substitution Principle
If $A = B$, then $A$ can be replaced by $B$ in any expression or equation.
This principle is fundamental to the substit...
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Challenging
A piggy bank contains nickels and dimes with a total value of $1.95. If the number of nickels and the number of dimes were swapped, the new total value would be $2.40. How many nickels were there originally?
A.10
B.19
C.21
D.15
Challenging
A jar has 40 coins, consisting of dimes and quarters, worth $7.00. The coins weigh a total of 150 grams. How many dimes are in the jar?
A.10
B.15
C.20
D.25
Easy
A problem states: 'A piggy bank has some nickels and dimes.' If 'n' represents the number of nickels, what does the variable 'd' most likely represent?
A.The value of the dimes
B.The total number of coins
C.The number of dimes
D.The number of dollars
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