急. 2o點.小六平均數

Ａ和Ｂ的平均數是６０, (A+B)/2 = 60

Ｂ和Ｃ的平均數是９０，(B+C)/2 = 90

Ｃ和Ａ的平均數是７０。(C+A)/2 = 70

三式相加 :

(A+B)/2 + (B+C)/2 + (C+A)/2 = 60 + 90 + 70

(2A + 2B + 2C)/2 = 220

A + B + C = 220

求Ａ、Ｂ和Ｃ的總值 220

Ａ和Ｂ的平均數是６０==> (Ａ+Ｂ) / 2 =60
Ｂ和Ｃ的平均數是９０==> +(B + C)/2=90
Ｃ和Ａ的平均數是７０==> (C + A)/2 =70

(Ａ+Ｂ) / 2 +(B + C)/2 + (C + A)/2 = 60 +90 + 70
((Ａ+Ｂ) +(B + C)+ (C + A) ) /2 = 220
(( A + B + C)* 2)/2 = 220
A + B + C = 220

90*2-60*2
=60(C大過A 60)

70*2-60*2
=20(C大過B 20=B大過A 40 )

SO

60+40除2=B
或
90-20除2=B
B=80

60-40除2=A
或
70-60除2=A
A=40

90+20除2=C
或
70+60除2=C
C=100

A+B+C=80+40+100
=220

(a+b)/2=60
(a+b)/2X2=60X2
a+b=120
(b+c)/2=90
(b+c)/2X2=90X2
b+c=180
(c+a)/2=70
(c+a)/2X2=70X2
c+a=140
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a+b=120
b+c=180
c+a=140
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a+b+b+c+c+a=440
2a+2b+2c=440
2a+2b+2c/2=440/2
a+b+c=220
_________________
A+B+C=220