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  2. Birthday problem - Wikipedia

    en.wikipedia.org/wiki/Birthday_problem

    From a permutations perspective, let the event A be the probability of finding a group of 23 people without any repeated birthdays. Where the event B is the probability of finding a group of 23 people with at least two people sharing same birthday, P(B) = 1 − P(A).

  3. Pi - Wikipedia

    en.wikipedia.org/wiki/Pi

    The number π (/ p aɪ /; spelled out as "pi") is a mathematical constant, approximately equal to 3.14159, that is the ratio of a circle's circumference to its diameter.It appears in many formulae across mathematics and physics, and some of these formulae are commonly used for defining π, to avoid relying on the definition of the length of a curve.

  4. Slide rule - Wikipedia

    en.wikipedia.org/wiki/Slide_rule

    The simplest case is for continuously compounded interest. Example: Taking D as the interest rate in percent, slide the index (the "1" at the right or left end of the scale) of C to the percent on D. The corresponding value on LL2 directly below the index will be the multiplier for 10 cycles of interest (typically years).

  5. Economics - Wikipedia

    en.wikipedia.org/wiki/Economics

    The earlier term for the discipline was "political economy", but since the late 19th century, it has commonly been called "economics". [22] The term is ultimately derived from Ancient Greek οἰκονομία (oikonomia) which is a term for the "way (nomos) to run a household (oikos)", or in other words the know-how of an οἰκονομικός (oikonomikos), or "household or homestead manager".

  6. Biology - Wikipedia

    en.wikipedia.org/wiki/Biology

    The simplest form of an organic molecule is the hydrocarbon, which is a large family of organic compounds that are composed of hydrogen atoms bonded to a chain of carbon atoms. A hydrocarbon backbone can be substituted by other elements such as oxygen (O), hydrogen (H), phosphorus (P), and sulfur (S), which can change the chemical behavior of ...

  7. Steam engine - Wikipedia

    en.wikipedia.org/wiki/Steam_engine

    The simplest valve gears give events of fixed length during the engine cycle and often make the engine rotate in only one direction. Many however have a reversing mechanism which additionally can provide means for saving steam as speed and momentum are gained by gradually "shortening the cutoff " or rather, shortening the admission event; this ...

  8. Economic history of the United States - Wikipedia

    en.wikipedia.org/wiki/Economic_history_of_the...

    From 1871 to 1913, "the average U.S. tariff on dutiable imports never fell below 38 percent [and] gross national product (GNP) grew 4.3 percent annually, twice the pace in free trade Britain and well above the U.S. average in the 20th century," notes Alfred Eckes Jr, chairman of the U.S. International Trade Commission under President Reagan. [53]