mental math
mental math articles on the Math Mental blog, with worked examples solved step by step.
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How to calculate percentages in your head: 10%, 1% and growth factors
To find x% of a value, multiply the value by x/100. In your head, start from 10% (divide by 10) and 1% (divide by 100) and combine them: 15% = 10% + 5%. For increases and discounts, multiply by the factor: +20% is ×1.2 and −20% is ×0.8.
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Fractions: how to add, subtract, multiply and divide, with examples
Add and subtract fractions with a common denominator, multiply by cross-canceling and divide by the reciprocal. Mixed numbers and worked examples included.
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