The everyday workhorses: the percentage calculator handles all three forms of every percentage problem (plus reverse percentages and the percent-vs-percentage-points trap), the ratio calculator scales recipes and splits amounts, and the average calculator computes mean, median, mode and standard deviation — and explains when each one lies.

The number-theory trio interlocks: fractions need common denominators, which come from the LCM & GCD calculator, whose Venn-diagram logic rests on prime factorization — three tools, one underlying structure. For chance and counting, the probability calculator covers dice, cards and the birthday paradox. The scientific calculator brings trig, logs and memory (with a guide to the degree/radian trap), and the Roman numeral converter handles MMXXVI and friends.

Each page teaches the method alongside the answer — worked examples, the classic mistakes, and why the rules work — so the tool doubles as the lesson.