[Arts] The number of primary colors (pigments) in painting: blue, red and yellow.
The number of secondary colors in painting: green (mixing of yellow and blue with equal amount), orange (red and yellow) and violet (red and blue).
The number of tertiary colors as well.
[Biology] The number of phalanges (joints) of each finger (except the thumb) and of each smaller toe (except the big toe): distal phalange (at the end, having nail), middle phalange and proximal phalange. The thumb and big toe have only 2 phalanges (no middle phalange).
[Biology] The number of tiny bones in each human ear: incus (anvil), malleus (hammer) and staples (stirrup).
[Biology] The number of genders: masculine, feminine and neuter.
[Biology] Tridactyl means having 3 toes, claws or similar parts on each limb. (Greek: tridaktulos is 3-fingered).
[Chemistry] The atomic number of Lithium (Li).
[Education] The number of points to which a course’s grade B is transferred, when computing a student’s GPA (general point average) in the popular 4.0-scale GPA system of most schools. A sign +/– may add/subtract .3 or 0.33 to the basic point, depending on schools.
[Education] The number of separate levels of graded schools for 12 grades before college in most countries: elementary, middle and high school.
[Education] Three R’s mean 3 basic learning skills for elementary students: Reading, writing and arithmetic.
[Education] A 3rd year college or high school student is a junior.
[EECS] The digit represented by the orange color by either first 2 bands or the exponent of 10 represented by that color of the 3rd band (i.e. multiplier is 103) in the electronic resistor/capacitor color code.
[Game] The size of a tic-tac-toe game board is: 3´3. A player wins by connect 3 alike symbols (X’s or O’s) in a straight line, either horizontal, vertical or diagonal.
[Game] The number of lines (broken and unbroken) in each of 8 trigrams or Pa-kua symbols/markings (for Korean or Chinese).
[Game] Sudoku is played on a 9×9 grid, which is divided into nine 3×3 boxes. The object is to fill it so that every row, column and 3×3 box contains each of 9 digits 1-9 once.
[Geology] U.S. cities/towns whose names start with “Three”: Three Bridges, New Jersey 08887 – Three Brothers, AR – Three Creek, Idaho 83301 – Three Forks, Kentucky 42159 – Three Forks, Montana 59752 – Three Lakes, Florida 33186 – Three Lakes, Washington 98290 – Three Lakes, Wisconsin 54562 – Three Oaks, Michigan 49128 – Three Points, Arizona 85736 – Three Springs, Kentucky 42746 – Three Springs, Pennsylvania 17264 – Threelinks, Kentucky 40456 and 6 towns named “Three Rivers” in 6 states: California 93271, Massachusetts 01080, Michigan 49093, New Mexico 88352, Oregon 97707 and Texas 78071.
[Language] Prefixes: Triple-, Tri-, Trio-, Triad-, Ternary-…
[Language] The number of English words with the double letter “uu”: continuum, residuum and vacuum.
[Language] The number of English words with all 5 vowels in alphabetical order: facetious, abstemious and arsenious.
[Language] The number of main parties in conversation in most languages: 1st (I, we), 2nd (you) and 3rd party (it, he, she, they).
[Language] The number of degrees of comparison: positive, comparative and superlative.
[Language] The maximum number of consecutive double letters in an English word: bookkeeping and bookkeeper(s).
[Language] There are usually 3 parts of a full name (complete name): last (or family) name, first (or given) name and middle name.
[Library] ISBN-3 is the International Standard Book Number for books published in German (Germany, Austria and Switzerland).
[Library] ISBN-0-03 is the International Standard Book Number for books published by Saunders College Publishing (or Harcourt Brace College Publishers).
[Literature] “Three Musketeers” by Alexander Dumas.
[Medical] In doctor’s prescription, “bid “ means “twice a day”, “tid” means “three times a day” and “qid”, “four times a day”, from Latin phrases “bis in die”, “ter in die” and “quarter in die”, respectfully.
[Military] A lieutenant general is called 3-star general (U.S. military).
[Money] The number of letters in the standard currency code of each country in the world. The currency codes are maintained by the International Organization for Standardization (ISO) in the Standard 4217. Examples: MNT for Mongolia, THB for Thailand, USD for U.S., ZAR for South Africa.
[Money] A JCB credit card number starts with either 2131 or 1800 (15-digit card) or 3 (for 16-digit card).
[Movie] Names of TV shows/series or movies: “Three Company”, “3rd Rock from the Sun”, “The Third Miracle”, “The Three Musketeers”, “Three Seasons”, “Three Amigos”, “Three of Hearts”, “Three Kings”, “Three Ninjas”, “Three Men and a Little Lady”, “Three Men and a Baby”, “Three Fugitives”, “Three Days of Rain”, "The Three Burials of Melquiades Estrada" and the series “Three Colors: Blue”, “Three Colors: Red”, “Three Colors: White” and “3:10 to Yuma”. And specially: "NUMB3RS".
[Music] The number of main music clefs: C-clef (Do), F-clef (Fa) and G-Clef (Sol).
[Phone] The digit that can be dialed mnemonically by either letter D, E or F on the telephone keypad.
[Phone] The number to key in text messaging on telephone keypad for letter D.
[Theology] God has 3 equal positions: Son (Jesus Christ), Father (God) and the Holy Spirit.
[Theology] January 6 is the Three Kings Day, the day three wise men visited the baby Jesus, which is as important as Christmas in Mexico, Puerto Rico, Spain and many Latin America countries. (Also known as Epiphany).
[Theology] Three represents a perfect harmony: the union of unity (one) and diversity (two).
[Phone] The emergency telephone number dialing within Kazakhstan, Turkmenistan and Uzbekistan and Tajikistan is 03 (Ambulance only).
[Library] First 3 digits (000, 001, 002 and 003) in the Dewey Decimal Classification System call numbers for library books in General Knowledge.
[Tirvia] The “Pi Day” is celebrated on 03/14 at 1:59:26PM. (See Number 3 in Math.)
3.0, 3.3, 3.6 and 3.9
[EECS] 3.0, 3.3, 3.6 and 3.9(W, KW or MW) are four of standard numerical values for resistors (of tolerance class 5%) between 3 and 4(W, KW or MW). 3.3mF (microfarads) is one of standard numerical values for capacitors.
[Trivia] Economic growth between 2.5% and 3.5% is typically viewed as the norm for a healthy economy in the United States.