GCD and LCM: faster alternative methods
The Euclidean algorithm, the product/GCD formula, and step-by-step GCD and LCM calculations for three numbers.
ReadMathematics
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Clear, organized learning paths that build strong foundations in mathematics and computer science.
Arithmetic
The four signs: operations in a row
Use +, −, × and ÷ once each: 42 challenges about intermediate results, including fractions.
ReadMathematical darts: three throws, every combination
One number board, exactly three throws and 36 challenges: from addition to a systematic search for combinations.
ReadTelescoping sums and products: fractions that cancel
A decomposition turns long sums and products into a few surviving terms: nine examples, six exercises and step-by-step solutions.
ReadFrom the compound rule of three to the Production-Resources-Time triple
A method for turning compound proportionality into a sequence of simple steps
ReadPercentage change and negative values
When -50% means an increase: the limitation of the traditional formula, the role of absolute value and the distinction between value and distance from zero.
ReadFractions, finally made visible
A fraction of a whole, a fraction of a fraction, and recovering the whole: visual examples and 25 problems with hints and solutions.
ReadFrom a fraction to a percentage
A path from ratios and equivalent fractions to the idea that a percentage is simply a fraction with denominator 100.
ReadSuccessive percentage changes
How to combine two percentage increases or decreases, why percentages cannot simply be added, and what happens when the two changes are opposites.
ReadPercentages: from meaning to the return to the original value
What % means, how to convert numbers and fractions, how increases and discounts combine, and which percentage reverses a previous change.
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Logic
From logarithm to algorithm: the hidden science of anagrams
Words meet permutations and computational thinking: learn to count, check and invent anagrams without losing a single letter.
Read5×5 Pentadoku: five regions, three rules
Solve Pentadoku with rows, columns and irregular regions. Worked example, strategies and interactive lab.
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