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  2. List of mathematical constants - Wikipedia

    en.wikipedia.org/wiki/List_of_mathematical_constants

    A mathematical constant is a key number whose value is fixed by an unambiguous definition, often referred to by a symbol (e.g., an alphabet letter), or by mathematicians' names to facilitate using it across multiple mathematical problems. [1]

  3. 68–95–99.7 rule - Wikipedia

    en.wikipedia.org/wiki/68–95–99.7_rule

    For illustration, if events are taken to occur daily, this would correspond to an event expected every 1.4 million years. This gives a simple normality test : if one witnesses a 6 σ in daily data and significantly fewer than 1 million years have passed, then a normal distribution most likely does not provide a good model for the magnitude or ...

  4. Percent sign - Wikipedia

    en.wikipedia.org/wiki/Percent_sign

    The percent sign % (sometimes per cent sign in British English) is the symbol used to indicate a percentage, a number or ratio as a fraction of 100. Related signs include the permille (per thousand) sign ‰ and the permyriad (per ten thousand) sign ‱ (also known as a basis point), which indicate that a number is divided by one thousand or ten thousand, respectively.

  5. Percentage - Wikipedia

    en.wikipedia.org/wiki/Percentage

    In general, if an increase of x percent is followed by a decrease of x percent, and the initial amount was p, the final amount is p (1 + 0.01 x)(1 − 0.01 x) = p (1 − (0.01 x) 2); hence the net change is an overall decrease by x percent of x percent (the square of the original percent change when expressed as a decimal number).

  6. Irreducible fraction - Wikipedia

    en.wikipedia.org/wiki/Irreducible_fraction

    The final result, ⁠ 4 / 3 ⁠, is an irreducible fraction because 4 and 3 have no common factors other than 1. The original fraction could have also been reduced in a single step by using the greatest common divisor of 90 and 120, which is 30. As 120 ÷ 30 = 4, and 90 ÷ 30 = 3, one gets = Which method is faster "by hand" depends on the ...

  7. Parts-per notation - Wikipedia

    en.wikipedia.org/wiki/Parts-per_notation

    For example, the conversion factor between a mass fraction of 1 ppb and a mole fraction of 1 ppb is about 4.7 for the greenhouse gas CFC-11 in air (Molar mass of CFC-11 / Mean molar mass of air = 137.368 / 28.97 = 4.74). For volume fraction, the suffix "V" or "v" is sometimes appended to the parts-per notation (e.g. ppmV, ppbv, pptv).

  8. Repeating decimal - Wikipedia

    en.wikipedia.org/wiki/Repeating_decimal

    For example, in duodecimal, ⁠ 1 / 2 ⁠ = 0.6, ⁠ 1 / 3 ⁠ = 0.4, ⁠ 1 / 4 ⁠ = 0.3 and ⁠ 1 / 6 ⁠ = 0.2 all terminate; ⁠ 1 / 5 ⁠ = 0. 2497 repeats with period length 4, in contrast with the equivalent decimal expansion of 0.2; ⁠ 1 / 7 ⁠ = 0. 186A35 has period 6 in duodecimal, just as it does in decimal. If b is an integer base ...

  9. Ratio - Wikipedia

    en.wikipedia.org/wiki/Ratio

    For example, the ratio 4:5 can be written as 1:1.25 (dividing both sides by 4) Alternatively, it can be written as 0.8:1 (dividing both sides by 5). Where the context makes the meaning clear, a ratio in this form is sometimes written without the 1 and the ratio symbol (:), though, mathematically, this makes it a factor or multiplier .