Three Science classes A, B and C take a Life Science test. The average score of students of class A is 83. The average score of students class B is 76. The average score of class C is 85. The average score of class A and 8 is 79 and average score of class B and C is 81. Then the average score. Of classes A, B and C is

• A/n=83
  A=83n
  B/m=76
  B=76m
  C/k=85
  C=85k
  (A+B)/(m+n)=79
  83n+76m=79n+79m
  4n=3m
  n=3m/4
  (B+C)/(m+k)=81
  76m+85k=81m+81k
  5m=4k
  m=4k/5 k=5m/4
  (A+B+C)/(m+n+k)=(83n+76m+85k)/(m+n+k)
  =(83(3m/4)+76m+85(5m/4))/(m+3m/4+5m/4) = 978m/12m
  = 81.5
• 6 years agoHelpfull: Yes(4) No(0)
• (a+b+c)/3=(83+79+85)/3=81.33
• 6 years agoHelpfull: Yes(2) No(0)
• (a+b+c)/3=(83+79+85)/3=81.33
• 6 years agoHelpfull: Yes(2) No(0)
• A/n=83
  A=83n
  B/m=76
  B=76m
  C/k=85
  C=85k
  (A+B)/(m+n)=79
  83n+76m=79n+79m
  4n=3m
  n=3m/4
  (B+C)/(m+k)=81
  76m+85k=81m+81k
  5m=4k
  m=4k/5 k=5m/4
  (A+B+C)/(m+n+k)=(83n+76m+85k)/(m+n+k)
  =(83(3m/4)+76m+85(5m/4))/(m+3m/4+5m/4) = 978m/12m
  = 81.5
• 6 years agoHelpfull: Yes(1) No(0)
• (83+75+85)/3=81.33
• 6 years agoHelpfull: Yes(1) No(0)
• A/n=83
  A=83n
  B/m=76
  B=76m
  C/k=85
  C=85k
  (A+B)/(m+n)=79
  83n+76m=79n+79m
  4n=3m
  n=3m/4
  (B+C)/(m+k)=81
  76m+85k=81m+81k
  5m=4k
  m=4k/5 k=5m/4
  (A+B+C)/(m+n+k)=(83n+76m+85k)/(m+n+k)
  =(83(3m/4)+76m+85(5m/4))/(m+3m/4+5m/4) = 978m/12m
  = 81.5
• 6 years agoHelpfull: Yes(0) No(0)
• A=83n
  B/m=76
  B=76m
  C/k=85
  C=85k
  (A+B)/(m+n)=79
  83n+76m=79n+79m
  4n=3m
  n=3m/4
  (B+C)/(m+k)=81
  76m+85k=81m+81k
  5m=4k
  m=4k/5 k=5m/4
  (A+B+C)/(m+n+k)=(83n+76m+85k)/(m+n+k)
  =(83(3m/4)+76m+85(5m/4))/(m+3m/4+5m/4) = 978m/12m
  = 81.
• 6 years agoHelpfull: Yes(0) No(0)
• (a1+a2+a3....an)/x =83
  (b1+b2b3......bn)/y=76
  (c1+c2+c3......cn)/z =85
  
  ((a1+a2+a3....an)+(b1+b2b3......bn))/ x+y =79
  
  ((b1+b2b3......bn)+(c1+c2+c3......cn)) / y+z =81
  
  solving above equations
  4x=3y && 4z=5y
  
  now
  (a1.....an+b1......bn+c1....cn)/(x+y+z)
  i.e ( 83x+76y+85z)/x+y+z
  ans.
  81.5
• 6 years agoHelpfull: Yes(0) No(0)
• a,b,c be number of students in class A,B,C respectively.
  given:A/a=83 ------------>(1)
  B/b=76------------->(2)
  C/c=85------------->(3)
  A+B/a+b=79-------->(4)
  B+C/b+c=81--------->(5)
  To Find: average=A+B+C/a+b+c
  SOLUTION:
  average=83a+76b+85c/(a+b+c)-------------------->(6)
  Now,
  In (4) substitute values of A and B from (1) and (2)
  we get, 83a+76b=79a+79b
  4a=3b
  b=4a/3 -------------------->(7)
  In (5) substitute B and C from (2) and (3) respectively,
  We get:76b+85c=81b+81c
  4c=5b
  c=5b/4
  c=5(4a/3)/4
  c=5a/3 ---------------------->(8)
  substitute (7) and (8) in (6)
  average=(83a+76*4a/3+85*5a/3)/(a+4a/3+5a/3)
  average=978a/12a
  average=81.5
  so,answer is 81.5
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