(fourth grade) Math Problem:
A mother is 25 years older than her son.
In 7 years, the mother will be 5 times older than her son.
Where is the son's father?
Let the child's age be c years and the mother's age be m years.
Now, m = c + 25.
In 7 years, m + 7 = 5 * (c + 7).
Substituting the first equation into the second one, we get
c + 32 = 5c + 35, from which 4c = -3, or c = -0.75.
So the child is minus nine months old, therefore the father is most probably in the mother.