Numbers and Number Systems - Britannica Kids

A number is a basic unit of mathematics. Numbers are used for counting, measuring, and comparing amounts. A number system is a set of symbols, or numerals, ... 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KindsofNumbersNumberscanbeclassifiedinmanyways.Thesimplestclassisthenatural,orcounting,numbers(1,2,3,…).Withtheadditionof0,theseareknownasthewholenumbers.Thenaturalnumbersarealsocalledpositivenumbersbecausetheyaregreaterthan0.Foreachofthepositivenumbers,thereisalsoanegativenumber(−1,−2,−3,…).Negativenumbersarelessthan0.Thenaturalnumbers,theirnegativeequivalents,and0makeupthesetofnumberscalledintegers.Theintegerscanbepicturedaspointsonalinethatcontinuesforeverinbothdirections.Fractionsarenumbersthatrepresentpartsofawhole.Fractionsarewrittenasdigitsseparatedbyaline,asin3/4.Thedigitbelowthelineiscalledthedenominator.Thedigitabovethelineiscalledthenumerator.Inreadingafraction,thenumeratorisstatedfirst.Forexample,3/4isreadas“three-fourths.”Fractionscanbeshownonanumberline,too.Fractionscanalsobewritteninaformcalleddecimals.Decimalsarewrittenusingthedigits(0–9)alongwithadotcalledadecimalpoint.Afractioncanbechangedtoadecimalbydividingthenumeratorbythedenominator.Inthisway,3/4canbechangedtothedecimal0.75. AncientNumberSystemsThefirstsystemofnumberswasprobablythetallysystem.Inthissystemaseparatemarkwasmadeforeveryitembeingcounted.Thissystemwasusefulonlywithsmallnumbers.TheancientEgyptiansdevelopedacomplexsystemforwritinglargenumbersinsymbolscalledhieroglyphics.Therewasasinglehieroglyphicsymbolforthenumber1,000.Buttowritethenumber999,itwasnecessarytowritethesymbolfor100ninetimes,thenthesymbolfor10ninetimes,andfinallythesymbolfor1ninetimes.TheancientRomansusedletterstorepresentnumbers—Ifor1,Vfor5,Xfor10,Lfor50,Cfor100,Dfor500,andMfor1,000.ThissystemisknownasRomannumerals.InRomannumerals,256iswrittenasCCLVI. Base-tenandOtherSystemsThemostcommonnumbersystemusedtodayiscalledthebase-ten,ordecimal,system.Ithas10digits(0–9)thatcanbecombinedtowriteanynumber.Thebase-tensystemwasinventedbyHindusinancientIndia.Later,Arabsimprovedthesystem.Forthisreasonthedigits0–9arecalledHindu-Arabicnumerals.Inthebase-tensystem,thevalueofeachdigitisbasedonitsposition,or“place,”inanumber.Thereisa“onesplace,”a“tensplace,”a“hundredsplace,”andsoforth.Inthenumber456,forexample,the4isinthehundredsplace,the5isinthetensplace,andthe6isintheonesplace.Writteninanotherway,thenumber456actuallyrepresents(4×100)+(5×10)+(6×1).Forsomepurposesothernumbersystemsaremoreusefulthanbase-ten.Forexample,computersusethebase-two,orbinary,numbersystem.Insteadof10digits,thissystemusesonlytwo—0and1.Inacomputerthesenumbersstandfor“off”and“on,”theonlytwopossiblestatesofthecomputer’selectricswitches. Print(SubscriberFeature) Email(SubscriberFeature) Translate(SubscriberFeature) Cite(SubscriberFeature) × It’shere:theNEWBritannicaKidswebsite! 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