아래는 각 계산기의 목적과 가정, 흔한 오류를 한 문단으로 정리한 가이드입니다. 결과 해석에 영향을 주는 전제를 먼저 확인하세요.
The Average Calculator computes the key statistical measures for any list of numbers: arithmetic mean (the sum divided by the count), median (the middle value), mode (the most frequent value), and range (max minus min). Enter your values separated by commas and get instant results — no spreadsheet required. These four measures together give you a complete picture of your data distribution. The mean is sensitive to outliers; the median is more robust. Knowing which measure to use in a given context is as important as calculating it correctly.
Percentages appear in everyday decisions more often than most people realize: a 30% discount, a 7% sales tax, a 15% service tip, a 5% annual raise, a 12% investment return. This calculator handles the three most common percentage questions in one tool: finding X% of a number (e.g., 20% of $150 = $30), finding what percentage one number is of another (e.g., 45 out of 180 = 25%), and finding a value after a percentage increase or decrease (e.g., $80 after a 15% discount = $68). If you need to calculate how much something changed between two values — for example, a stock moving from $120 to $150 — use the Percentage Change Calculator instead. If you need to apply a percentage growth rate repeatedly over time, use the Compound Interest Calculator.
The Percentage Change Calculator finds the exact percentage increase or decrease between two values. Whether you're analyzing a price change, comparing this year's revenue to last year, tracking weight loss progress, or calculating a salary raise percentage, the formula is the same: divide the change by the original value and multiply by 100. This calculator also handles the reverse — enter a starting value and a desired percentage change to find the new value. Understanding percentage change is one of the most practical math skills for finance, business, and daily life.
The Random Number Generator draws uniform random integers (or decimals, when the UI offers them) within bounds you set — useful when you need repeatable “pick a number” logic without building a spreadsheet macro. Choose min/max, how many draws, and whether duplicates are allowed; browsers that support the Web Crypto API use a stronger RNG than `Math.random` for draws, but this tool is still aimed at everyday use (games, classroom picks, rough sampling), not audited lotteries or cryptographic key material. Typical uses: lottery-style picks, simple random assignment, quick Monte Carlo intuition, and fair tie-breaks. Everything runs locally — no server round-trip.
The Ratio Calculator helps you simplify ratios to their lowest terms, solve proportions for missing values, scale ratios up or down, and check if two ratios are equivalent. Ratios express the relationship between two quantities and appear everywhere in daily life: cooking recipes (double the batch), map scales (1:50,000), financial ratios (price-to-earnings), aspect ratios (16:9 for HD video), and mixing solutions (1 part concentrate to 4 parts water). This calculator handles all standard ratio operations with clear step-by-step results.