Study Guides
Answer first, then a worked example, then the common wrong answer. Each guide links to the CalcSolver tools that match the topic.
Calculator
How to Use a Scientific Calculator
The keys that matter, in the order you'll use them, with examples you can check.
Updated October 2, 2026
Trigonometry
Degrees vs Radians Explained
When to use each, how to convert, and a 5-second test for your calculator.
Updated October 2, 2026
Percent
Percent Problems: 5 Traps to Avoid
Discounts, growth and percentage points, with the wrong answer next to the right one.
Updated October 2, 2026
Algebra
The Remainder Theorem Made Simple
Skip long division. Put the root in and read off the remainder.
Updated October 2, 2026
Fractions
Fractions as Decimals and Percents
1/3, 6/7 and 7/8 explained, plus why 0.33 × 3 isn't 1.
Updated October 2, 2026
Number theory
How to Test for a Prime Number
Divisibility rules and the square-root shortcut, with 91 as the classic trap.
Updated October 2, 2026
Calculator
Why Calculators Show Tiny Errors
What 1.2246e-16 means, why π can't be stored exactly, and how display rounding helps.
Updated October 2, 2026