Three years ago, the average age of a family of 5 members was 21 years. A baby having been born, the average age of the family is again 20.5 years. The present age of the baby is?
Explanation:
Average age of 5 members 3 years ago = 21 years. Average age of these 5 members today = 21 + 3 = 24 years. ⇒ Total age of these 5 members (excluding the baby) = 24 × 5 = 120.
⇒ Total age of all 6 members (including the baby) = 20.5 × 6 = 123.
∴ 123 = 120 + baby’s age ⇒ Baby’s age = 3 years.
Hence, option (a).
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