Multiple choice

There are 5 older and some children living in a family, thus the average age of their family is 28 years. If the average age of elders and children is 42 years and 18 years respectively, then how many children are there in the family?

  1. 5

  2. 8

  3. 7

  4. 6

  5. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let number of children be x. Total people = 5 + x. Using weighted average: (5×42 + x×18)/(5 + x) = 28. Solving: 210 + 18x = 28(5 + x) = 140 + 28x. So 210 - 140 = 28x - 18x, giving 70 = 10x, therefore x = 7. There are 7 children in the family.

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