Arithmetic
Sal Khan
Master basic arithmetic! Learn addition, subtraction, multiplication, and division with expert instruction from Sal Khan.
More resources on Basic Operations
Wolfram MathWorld
MathWorld is an online mathematics encyclopedia from Wolfram Research offering detailed, browsable articles on topics across the math spectrum, including algebra, geometry, calculus, and number theory. Each entry includes definitions, theorems, formulas, diagrams, worked examples, and links to further reading.
IXL - Basic Operations Practice
Skill-by-skill practice site from IXL Learning covering third-grade math, including multiplication and division facts, multi-digit addition and subtraction, and word problems. Students get instant feedback and explanations; free use is capped at a few questions daily without a subscription.
Arithmetic for Teachers
Textbook from the American Mathematical Society for prospective elementary teachers, rebuilding whole numbers, integers, and decimals from their foundations using the number line. Readers learn to justify standard algorithms and explain why arithmetic works, with applications and geometry topics.
Basic Mathematics
Rigorous precalculus text by Serge Lang covering numbers, linear and quadratic equations, Euclidean and coordinate geometry, trigonometry, functions, complex numbers, induction, and determinants. Readers build proof-based fluency in foundational mathematics as preparation for calculus and linear algebra.
mathsisfun.com
MathIsFun.com is a beginner-friendly math site that explains concepts with clear, step-by-step lessons and interactive activities. It covers topics from algebra and linear equations to geometry, fractions, data, and more, with practice problems, worksheets, and quizzes.