What Is Percentage Calculation?
Understand what percentages mean, how the core formula works, and when to use it.
PercentagesHow to Calculate Percentage Increase
Learn the percentage increase formula with price, salary, and growth examples.
PercentagesPercentage Decrease Explained
Calculate decreases accurately and avoid common baseline mistakes.
PercentagesPercentage Difference vs. Percentage Change
Choose the right comparison formula when values have or do not have a baseline.
AveragesHow to Calculate an Average: Formula, Steps, and Examples
Calculate the arithmetic mean from a sum and count, check the result, and solve useful reverse-average problems.
AveragesMean, Median, and Mode: Differences, Formulas, and When to Use Each
Compare mean, median, and mode, calculate each correctly, and choose a measure that fits the data and question.
AveragesHow to Calculate a Weighted Average: Formula and Examples
Calculate a weighted average with percentage, frequency, credit, price, or portfolio weights and handle edge cases correctly.
AveragesWhen an Average Can Be Misleading—and What to Check Instead
Recognize when a correct average hides outliers, skew, subgroups, sample-size differences, missing data, or changing definitions.
DatesHow Is Exact Age Calculated in Years, Months, and Days?
Learn how exact calendar age counts completed years, completed months, and remaining days across birthdays, month ends, and leap years.
DatesHow Leap Years Affect Age Calculations
Apply the Gregorian century rule and understand how February 29 changes elapsed-day totals without changing the meaning of completed age. Test ordinary leap years and century boundaries with explicit date intervals and independently checked totals across common-year and leap-year endpoints, including 1900, 2000, 2024, and 2100 in practical calendar calculations.