The average age of a couple is 25 years. The average age of the family just after the birth of the first child was 18 years. The average age of the family just after the second child was born was 15 years. The average age of the family after the third and the fourth children (who are twins) were born was 12 years. If the present average age of the family of six persons is 16 years, how old is the eldest child?

• m+f = 2*25 =50
  
  when 1st child was born
  (m+f+fc(0 at the time of born) )/3=18
  =>m+f = 54
  => fc born after (54-50)/2 = 2 years
  
  when 2nd child is born
  m+f+fc=54
  m=f+fc+2c(0 at the time of born) = 15*4 =60
  => (60-45)/3 (m+f+fc counted only bcoz 2c age is 0 at the time of birth)=2
  1st child is 2 years old and 2nd child is zero now
  
  similalrly when 3rd n 4th born both of their age will be zero and
  m+f+fc+2c =60
  (m+f+fc+2c+(3c+4c))/6 = 12
  =>ist son age increaed by (72-60)/4 =3 years
  now fc is 2+3 = 5 yrs old
  
  now 6 members => 16*6 = 96 yrs
  prev 72 yrs
  fc age increases by (96-72)/6=4 yrs
  => fc age will be 2+3+4 = 9 years
• 4 years agoHelpfull: Yes(12) No(2)
• Ans. 9 years
  
  m + f = 50
  m + f + I = 54 ------> (1)
  m + f + I + II = 60 ------> (2)
  m + f + I + II + III + IV = 72 ------> (3)
  m + f + I + II + III + IV = 96 ------> (4)
  
  (1) => 54 - 50 = 4 / 2 = 2 years gap in each
  => 27 + 27 + 0 = 54
  
  (2) => 60 - 54 = 6 / 3 = 2 years gap in each
  => 29 + 29 + 2 + 0 = 60
  
  (3) => 72 - 60 = 12 / 4 = 3 years gap in each
  => 32 + 32 + 5 + 3 + 0 + 0 = 72
  
  (4) => 96 - 72 = 24 / 6 = 4 years gap in each
  => 36 + 36 + 9 + 7 + 4 + 4 = 96
  
  Therefore, from above solution Eldest (Oldest/First) Child Age is 9 years.
• 3 years agoHelpfull: Yes(5) No(0)
• Mother age is m
  father age is f
  then,given (m+f)/2=25=m+f=50
  (m+f+fc)/3=m+f+fc=54
  fc=54-50=4
  on 2nd child birth=(m+f+fc+sc)/4=15
• 4 years agoHelpfull: Yes(2) No(5)
• ans will be 9
• 4 years agoHelpfull: Yes(0) No(2)