Question 935866
Let's define some variables.
{{{f}}}= age of the father/husband at the time of the marriage.
{{{m}}}= age of the mother/wife at the time of the marriage.
{{{s}}}= age of the son at the time of the marriage.
{{{d}}}= age of the daughter-in-law at the time of the marriage.
At the time of the marriage, the average age of a family comprising father/husband, mother/wife and their son was 42, so
{{{f+m+s)/3=42}}}<--->{{{f+m+s=42*3}}}<--->{{{f+m+s=126}}} .
After 1 year the newlyweds had a child,
and 5 years after that, meaning {{{1+5=6}}} years after the marriage,
the child was 5,
and everyone else was 6 years older.
The old husband/father was {{{f+6}}} ;
the old wife/mother was {{{m+6}}} ;
the married son was {{{s+6}}} , and
the daughter-in-law was {{{d+6}}} .
The average age for that 5-person family was
{{{((f+6)+(m+6)+(s+6)+(d+6)+5)/5=36}}}
{{{(f+m+s+d+6+6+6+6+5)/5=36}}}
{{{f+m+s+d+6+6+6+6+5=36*5}}}
{{{(f+m+s)+d+29=180}}}
{{{155+d=180}}}
{{{d=180-155}}}
{{{highlight(d=25)}}}