If the average age of the husband and wife was 23 years, 5 years ago, the sum of the ages as at then \(=23 \times 2=46\) yearst present, the sum of their ages will be
46 years \(+10\) years \(=56\) years
Let the age of the child be \(x\). Since the average age of the husband, wife and the child is 20 years, we have:
\begin{array}{l}
\frac{56+x}{3}=20 \\
56+x=60 \\
x=(60-56) \text { yeas }=4 \text { years }
\end{array}