The question that I am about to request for your help is almost similar to the one that appears [here](https://math.stackexchange.com/questions/960637/can-we-solve-variable-questions-without-using-algebra-for-example-age-problems).

However, I am stumped by the wording of the question as it appears in the pages of an old math book from where I picked it up.

> 
> Five years ago the sum of the ages of a father and his son was 40
> years. Five years hence, the age of the father will be 3 times the age
> of his son. Find their present ages.
> 
> 
> 

The solution is given thus (without using variables):

> 
> The sum of the present ages of the father and his son = $40+5+5=50$
> years.
> 
> 
> 5 years hence the sum of their ages will be = $50+5+5=60$ years.
> 
> 
> **But by the question, this sum is 4 times the age of the son;** Therefore, 5 years hence, the age of the son will be = $60 / 4 = 15$
> years and that of his father $60-15=45$ years.
> 
> 
> Therefore, the present ages of the father and son are $45-5=40$, and
> $15-5=10$ years, respectively.
> 
> 
> 

The part of the solution that I cannot understand is how is the statement - **But by the question, this sum is 4 times the age of the son** - arrived at?

Any help will be much appreciated.