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Copyright: 1996  2024 Webmaster:
Kirt Blattenberger,
BSEE  KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dialup modems blazed along at 14.4 kbps
while typing up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
All trademarks, copyrights, patents, and other rights of ownership to images
and text used on the RF Cafe website are hereby acknowledged.
My Hobby Website:
AirplanesAndRockets.com


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Permutations & Combinations 
In several fields of
mathematics the term permutation is used with different but closely related meanings. They all relate to the
notion of mapping the elements of a set to other elements of the same set, i.e., exchanging (or "permuting")
elements of a set.
In combinatorial mathematics, a combination is an unordered collection of distinct
elements, usually of a prescribed size and taken from a given set. (An ordered collection of distinct elements
would sometimes be called a permutation, but that term is ambiguous.) Given such a set S, a combination of
elements of S is just a subset of S, where, as always for (sub)sets the order of the elements is not taken into
account (two lists with the same elements in different orders are considered to be the same combination). Also, as
always for (sub)sets, no elements can be repeated more than once in a combination; this is often referred to as a
"collection without repetition". For instance, {1,1,2} is not a combination of three digits; as a set this is the
same as {1,2,1} or as {2,1,1}. On the contrary, a poker hand can be described as a combination of 5 cards from a
52card deck: the order of the cards doesn't matter, and there can be no identical cards among the 5.
 Wikipedia


Where: n = total number of items in the group R =
number of items chosen from the group


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