Multiple choice

Three years ago, the average age of a family of 8 members was 30 years. If one child is also included in the family, the present average age of the family remains the same. What is the present age of the child?

  1. 3 years

  2. 4 years

  3. 6 years

  4. 1 year
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Three years ago, sum of ages of 8 members = 8 * 30 = 240. Present sum of ages = 240 + (8 * 3) = 264. With the child, there are 9 members, and the average is still 30. Present sum = 9 * 30 = 270. Age of child = 270 - 264 = 6.

AI explanation

Three years ago, the average age of the 8 family members was 30 years, so their total age at that time was 8 multiplied by 30, equaling 240 years. In the present day, the total age of these same 8 members is 240 plus (8 multiplied by 3), which equals 264 years. Let the present age of the child be C; adding the child brings the total present age of the 9 members to 264 plus C. Since the present average age remains 30 years, the total present age of all 9 members is 9 multiplied by 30, equaling 270 years, so 264 plus C equals 270, which means the child's present age is 6 years.

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