Average unchanged after birth: Three years ago, a 5-member family averaged 17 years. Today, even after a child is born, the family’s average is still 17. Find the present age of the child.

Introduction / Context:
Similar to earlier average-over-time problems, we compare the current total with the projected total of the original members. The difference yields the child’s present age.

Given Data / Assumptions:

• 3 years ago: 5 members, average = 17 → total = 85
• Today: 6 members after birth, average still 17 → total = 6 * 17 = 102

Concept / Approach:
Increase in total for original five due to 3 years = 5 * 3 = 15. Add this to 85 to get the original-five total today, then compare with 102 to get the child’s age now.

Step-by-Step Solution:

Verification / Alternative check:
Total rise in the five members over 3 years is 15 years. The child must be 2 so that the six-person average remains 17 today.

Why Other Options Are Wrong:

• 1, 3, 2.5, 4: do not equate the present total to 102.

Common Pitfalls:
Forgetting to add the 3-year increment for each of the original five or miscomputing the current grand total for six members.

Final Answer:
2 yr