GMAT数学精解算术概述3
钱永强《GMAT数学精解》八描述统计descriptivestatistics1平均数averageorarithmeticmea
2中数media
Tocalculatethemedia
of
umbers，firstorderthe
umbersfromleasttogreatest；if
isodd，themedia
isdefi
edasthemiddle
umber，whileif
iseve
，themedia
isdefi
edastheaverageofthetwomiddle
umbersForthedata647104the
umbersi
orderare446710a
dthemedia
is6themiddle
umberForthe
umbers4668912themedia
is6827Notethatthemea
ofthese
umbersis75
f3众数mode：一组数中的众数是指出现频率的数。例：themodeof7，9，6，7，2，1is7。4值域ra
ge：表明数的分布的量，其被定义为值减最小值的差。例：thera
geof1，7，27，27，36is36137。5标准方差sta
darddeviatio
：O
eofthemostcommo
measuresofdispersio
isthesta
darddeviatio
Ge
erallyspeaki
gthegreaterthedataarespreadawayfromthemea
thegreaterthesta
darddeviatio
Thesta
darddeviatio
of
umbersca
becalculatedasfollows1fi
dthearithmeticmea
2fi
dthediffere
cesbetwee
themea
a
deachofthe
umbers3squareeachofthediffere
ces4fi
dtheaverageofthesquareddiffere
ces5takethe
o
egativesquarerootofthisaverageNoticethatthesta
darddeviatio
depe
dso
everydatavaluealthoughitdepe
dsmosto
valuesthatarefarthestfromthemea
Thisiswhyadistributio
withdatagroupedcloselyarou
dthemea
willhaveasmallersta
darddeviatio
tha
dataspreadfarfromthemea

f6排列与组合Therearesomeusefulmethodsforcou
ti
gobjectsa
dsetsofobjectswithoutactuallylisti
gtheeleme
tstobecou
tedThefollowi
gpri
cipleofMultiplicatio
isfu
dame
taltothesemethodsIfafirstobjectmaybechose
i
mwaysa
daseco
dobjectmaybechose
i
waysthe
therearem
waysofchoosi
gbothobjectsAsa
examplesupposetheobjectsareitemso
ame
uIfamealco
sistsofo
ee
treea
do
edesserta
dthereare5e
treesa
d3dessertso
theme
uthe
5×315differe
tmealsca
beorderedfromtheme
uAsa
otherexampleeachtimeacoi
isflippedtherearetwopossibleoutcomesheadsa
dtailsIfa
experime
tco
sistsof8co
secutivecoi
flipstheexperime
thas28possibleoutcomeswhereeachoftheseoutcomesisalistofheadsa
dtailsi
someorder☆阶乘：factorial
otatio
假如一个大于1的整数
，计算
的阶乘被表示为
，被定义为从1至
所有整数的乘积，例如：44×3×2×124注意：011
f☆排列：permutatio
sThefactorialisusefulforcou
ti
gthe
umberofwaysthatasetofobjectsca
beorderedIfasetof
objectsistobeorderedfrom1stto
ththereare
choicesforthe1stobject
1choicesforthe2
dobject
2choicesforthe3rdobjectr