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The average weight of a group of persons increased from 48 kg to 51 kg, when two persons weighing 78 kg and 93 kg join the group. Find the initial number of members in the group?

Correct answer: C. 23

  • A. 21
  • B. 22
  • C. 23
  • D. 24

Explanation

If the initial group had n persons, its total weight was 48n kilograms. After two persons weighing 78 kilograms and 93 kilograms join, the total is 48n + 171 kilograms, and the new total is 51(n + 2) kilograms. Thus 48n + 171 = 51n + 102, giving 3n = 69 and n = 23 persons. The likely error is using only one joining person's weight, which leads to a different option.

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