Five years ago, the average age of a husband and wife was 23 years. Now, the average age of the husband, the wife, and their child (born in the interim) is 20 years. How old is the child now?

Introduction:
Average age problems with shifting family sizes are best handled via total ages. Convert averages to totals at each time point, account for aging across years, and compare to deduce the newcomer’s current age.

Given Data / Assumptions:

• 5 years ago: average of 2 people = 23 → total then = 46
• Now: average of 3 people = 20 → total now = 60
• Husband and wife each aged 5 years over the interval

Concept / Approach:
Present total of the couple = past total + 2 * 5 = 46 + 10 = 56. Present family total (including the child) is 60, so the child’s current age is the difference 60 − 56.

Step-by-Step Solution:

Verification / Alternative check:
Five years ago child did not exist or was newly born later; totals align with averages exactly when using 4 years as the child’s age now.

Why Other Options Are Wrong:
3, 1, less than 1, and 5 years lead to totals that do not match the given averages simultaneously.

Common Pitfalls:
Averaging ages again after adding years or forgetting both adults gain 5 years each, not 5 years in total.

Final Answer:
4 year