How to Calculate Percentages Quickly and Accurately

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To calculate percentages quickly, start by converting the percentage to a decimal—just move the decimal two places left, like 15% becoming 0.15. Then multiply that by the whole number to find the part. For a reverse calculation, divide the part by the whole and multiply by 100 to get the percentage. Common shortcuts include using 10% as a base to easily find 5% or 20%.