Nine members of a family are standing in a row. Their average age is 70. The average age of the first four members in the row is 64 and the average age of the last seven members in the row is 80. What is the average age of the third and fourth member in the row?
  • a)
    78
  • b)
    86
  • c)
     93
  • d)
     89
  • e)
    87
Correct answer is option 'C'. Can you explain this answer?

CAT Question

By Ranjeet · Dec 27, 2019 ·CAT
2 Answers
Veera Reddy Konabhai answered 6 days ago
Consider first two members as set A, third person as B, fourth person as C and remaining five membes as set D.
given (A+B+C+D)/9 = 70 => A+B+C+D = 630
and (A+B+C)/4 = 64 => A+B+C = 256 ----> smt1
and (B+C+D)/7 = 80 => B+C+D = 560 ----->smt2
now add smt1 and smt2 that gives us A+B+C+B+C+D = 816 and given A+B+C+D is 630 subitting in previous equation we get B+C+630 = 816 and solving gives us B+C = 186. now we want avg of B,C that is (B+C)/2 = 186/2 = 93

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