Arithmetic Operations
64 concepts · ordered by prerequisite depth
Operations and arithmetic encompass the fundamental computational skills — addition, subtraction, multiplication, and division — along with the properties and strategies that make those computations efficient and meaningful. This topic goes well beyond rote memorization of facts. Students learn why the standard algorithms work, how properties like commutativity, associativity, and distributivity simplify calculations, and how to apply operations to increasingly complex number types including decimals and negative numbers. Order of operations provides a universal convention for evaluating expressions. Mental math strategies, estimation, and number sense are emphasized so that students can judge whether an answer is reasonable. These foundational skills are used in every subsequent math topic, from algebra to statistics, and in countless real-world tasks such as budgeting, cooking, and measuring.
Suggested order: Master single-digit facts and place-value understanding first, then learn multi-digit algorithms, properties of operations, and order of operations before applying these skills to decimals and negative numbers.
Start here
Addition
The arithmetic operation of combining two or more numbers into a single total, representing joining or accumulating quantities.
Open lesson
Subtraction
Finding the difference between two numbers by removing one quantity from another, or measuring the gap between them.
Open lesson
Multiplication
Finding the total when a quantity is repeated a given number of times; the result of repeated addition of equal groups.
Open lesson
Division
Splitting a quantity into equal parts, or finding how many times one number fits into another. Division answers two questions: 'How many in each group?' and 'How many groups?'
Open lesson
Continue from here · 60 concepts
Absolute Value
The distance of a number from zero on the number line, always non-negative; written $|x|$. For any real number, absolute value strips away the sign and returns only the magnitude.
Addition as Combining
Understanding addition as the act of joining or combining two or more quantities to form a larger whole amount. This model helps students see addition as a physical action rather than an abstract rule.
Balance Principle
The rule that any operation applied to one side of an equation must also be applied to the other side to preserve equality.
Bar Graphs
A chart that uses rectangular bars of different heights or lengths to represent and compare quantities, where each bar's length is proportional to the value it represents and categories are shown on one axis.
Cancellation
Cancellation is the process of removing a common factor from the numerator and denominator of a fraction, or from both sides of an equation, to simplify. It works because dividing both parts by the same nonzero number leaves an equivalent but simpler form.
Constant of Proportionality
The constant ratio $k$ between two proportional quantities: if $y = kx$, then $k$ is the constant of proportionality.
Constraints
Conditions or restrictions that limit which values are allowed in a problem. Constraints narrow the set of possible solutions, such as 'x must be positive' or 'the total cannot exceed 100.'
Decimal Place Value
The value assigned to each digit's position to the right of the decimal point: the first position is tenths ($\frac{1}{10}$), the second is hundredths ($\frac{1}{100}$), the third is thousandths ($\frac{1}{1000}$), and so on.
Equality as Relationship
Understanding $=$ not as 'the answer is' but as expressing that two expressions represent the same value.
Equivalence
When two expressions, numbers, or objects represent the same value or are interchangeable in every relevant context.
Inequality Intuition
Understanding that $<$ and $>$ describe ordering relationships—one quantity is strictly smaller or larger than the other.
Invariants
Quantities or properties that remain unchanged during a process, operation, or transformation—values that stay the same no matter how the system is rearranged or acted upon.
Length Measurement
Measuring how long something is using standard units (cm, m, in, ft) by finding the difference between start and end marks.
Linear Relationship
A relationship between two variables where the rate of change is constant, producing a straight line when graphed. Expressed as $y = mx + b$ where $m$ is the slope.
Monotonicity
A function or sequence that consistently moves in one direction only—always increasing or always decreasing throughout its domain.
Picture Graphs
A way of displaying data using pictures or icons, where each picture represents one unit (or a set number of units), and the total for each category is found by counting or multiplying the number of pictures by the scale value.
Simple Patterns
A repeating pattern is a sequence of elements (colors, shapes, numbers, or sounds) that repeats in a predictable cycle.
Telling Time
Reading analog and digital clocks to determine the current time in hours, half hours, quarter hours, and five-minute intervals.
Weight Measurement
Measuring how heavy something is using standard units such as grams, kilograms, ounces, and pounds, by comparing an object's weight against known reference amounts on a balance or scale.
Bounds
The upper and lower limits within which a quantity must lie; often expressed as $a \leq x \leq b$.
Direct Variation
A proportional relationship $y = kx$ that always passes through the origin — when one quantity doubles, so does the other.
Growing Patterns
A growing pattern is a sequence where each term increases by following a consistent rule, such as adding the same number each time (2, 5, 8, 11,...) or multiplying by a constant factor (3, 6, 12, 24,...). Recognizing the rule lets you predict any term in the sequence.
Money Counting
Identifying coins and bills by their value and adding them together to find a total amount of money.
Nonlinear Relationship
A relationship between two quantities where the rate of change is not constant—the graph is curved, not a straight line.
Skip Counting
Counting forward by a number other than 1, jumping by equal intervals such as 2s, 5s, or 10s to produce the multiples of that number.
Adding and Subtracting Decimals
Adding and subtracting numbers with decimal points by aligning the decimal points vertically so that digits with the same place value line up.
Associativity
A property where changing the grouping of operands does not change the result: $(a \star b) \star c = a \star (b \star c)$.
Commutativity
A property where swapping the order of two operands does not change the result: $a \ \star\ b = b\ \star\ a$.
Distributive Property
The rule that multiplying a sum equals the sum of individual products: $a(b+c) = ab + ac$. It links multiplication and addition, allowing you to break apart or combine terms.
Elapsed Time
Calculating the amount of time that passes between a start time and an end time, using hours and minutes in base-60 arithmetic rather than base-10.
Exponents
An operation representing repeated multiplication: $a^n$ means $a$ multiplied by itself $n$ times. For example, $2^3 = 2 \times 2 \times 2 = 8$. Exponents extend to zero, negative, and fractional powers.
Identity Elements
Special numbers that leave any other number unchanged under a given operation: 0 for addition, 1 for multiplication.
Making Change
Calculating how much money is returned to a buyer when they pay more than the purchase price, using subtraction with dollars and cents or the counting-up strategy.
Multi-Digit Addition and Subtraction
Adding and subtracting numbers with three or more digits using the standard algorithm, which involves regrouping (carrying) in addition and borrowing in subtraction.
Multi-Digit Multiplication
Multiplying numbers with two or more digits using the standard algorithm, partial products, or the area (box) model.
Multiplication as Area
Understanding multiplication as calculating the area of a rectangle: length times width gives the number of unit squares that fit inside. This visual model connects arithmetic to geometry.
Multiplication as Scaling
Understanding multiplication as resizing or scaling a quantity by a factor. Multiplying by 2 doubles, by 0.5 halves, and by 1 leaves unchanged — it stretches or shrinks the original number.
Multiplying Decimals
Multiplying numbers that contain decimal points by first multiplying as if they were whole numbers, then placing the decimal point in the product based on the total number of decimal places in both factors.
Proportional Reasoning
The ability to recognize and work with multiplicative relationships between quantities. If one quantity doubles, a proportional quantity also doubles — the ratio stays constant.
Repeated Operations
Applying the same operation multiple times in succession, where the repetition is often compressed into a higher-level operation: repeated addition becomes multiplication ($n \cdot a$), and repeated multiplication becomes exponentiation ($a^n$).
Subtraction as Difference
Understanding subtraction as finding the gap or difference between two quantities, rather than just 'taking away.' This comparison model asks 'how many more?' or 'how far apart?'
Tally Charts
A method of recording and organizing data by drawing tally marks grouped in sets of five, where four vertical lines are crossed by a fifth diagonal line.
Division as Inverse
Understanding division as the reverse of multiplication: if $a \times b = c$, then $c \div b = a$. This inverse relationship lets you undo multiplication to find missing factors.
Division as Sharing
Understanding division as distributing a total equally among a given number of groups. This 'fair sharing' model asks: if I share equally, how many does each group get?
Integer Operations
Adding, subtracting, multiplying, and dividing integers—numbers that include positive values, negative values, and zero.
Inverse Operations
Operations that undo each other: addition undoes subtraction, multiplication undoes division, and vice versa. Applying an operation followed by its inverse returns you to the starting value.
Inverse Variation
A relationship where $y = \frac{k}{x}$: as one quantity doubles, the other halves—their product stays constant.
Long Division
Long division is a step-by-step method for dividing large numbers by breaking the problem into a series of easier steps: divide, multiply, subtract, bring down, and repeat. It produces a quotient and possibly a remainder.
Operation Closure
A set is closed under an operation if performing that operation on members of the set always produces a result that is also in the set. For example, integers are closed under addition.
Operation Hierarchy
The layered relationship between arithmetic operations, where each is built from the previous: multiplication from addition, exponentiation from multiplication.
Order of Operations
The agreed-upon sequence for evaluating expressions: Parentheses, Exponents, Multiplication/Division (left to right), Addition/Subtraction (left to right).
Square Roots
The non-negative number $b$ such that $b^2 = a$, written $\sqrt{a} = b$ — the inverse of squaring.
Square vs Cube Intuition
Understanding $x^2$ as the area of a square with side $x$ (2D), and $x^3$ as the volume of a cube (3D).
Symmetry in Operations
When exchanging or swapping operands or roles in an operation produces the same result or a symmetrically related one.
Unit Rate
A rate expressed as a quantity per single unit of another quantity, such as miles per hour or cost per item.
Unknown Factor Problems
An unknown factor problem asks you to find a missing number in a multiplication equation, such as $? \times 6 = 48$ or $8 \times ? = 56$.
Word Problems
Word problems require translating a real-world scenario described in natural language into mathematical relationships, identifying the unknown quantity, setting up equations or expressions, and solving them to answer the question.
Dividing Decimals
Dividing numbers that contain decimal points, typically by converting the divisor to a whole number (multiplying both divisor and dividend by a power of 10) and then performing long division.
Operations with Rational Numbers
Extending addition, subtraction, multiplication, and division to the full set of rational numbers—including fractions, decimals, mixed numbers, and their negative counterparts.
Roots as Inverse Growth
Roots reverse the process of exponentiation: the $n$th root of $a$ finds the number that, raised to the $n$th power, produces $a$. For example, $\sqrt[3]{8} = 2$ because $2^3 = 8$.