OpenStax Prealgebra 2e — Chapter 3: Introduction to Integers
by Lynn Marecek, MaryAnne Anthony-Smith, Andrea Honeycutt Mathis · OpenStax (Rice University)
A free open-access chapter from Rice University's OpenStax Prealgebra, covering the number line, opposites, absolute value, and the four operations on integers. Worked examples and several hundred graded exercises with answers let you check your own work.
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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.