Multiple choice

4 years ago, the average age of a family of 5 memberswas 20 years. A baby having been born, the average age ofthe family is same today. The present age of the baby is?

  1. 0 year

  2. (3/2) years

  3. (7/2) years

  4. 2 years

  5. 4 years
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Four years ago, the sum of the ages of the 5 family members was 100 years. Today, each of those 5 members is 4 years older, making their sum 120 years. Since the average age of the 6-member family today is still 20 years, the total sum of their ages is 120 years, meaning the baby's age is 0 years.

AI explanation

Four years ago, the total age of the 5 family members was 5 times 20, which equals 100 years. Today, the total age of these same 5 members is 100 plus 5 times 4, which equals 120 years. Let the baby's age be x, so the new total age of the 6 members is 120 plus x, and the new average is (120 plus x) divided by 6. Since this new average is the same as the old average, we have (120 plus x) divided by 6 equals 20, which means 120 plus x equals 120, making the baby 0 years old today.

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