Question 281515
These word problems are always tricky, basically you want to set up two equations in order to find both their ages.

From the first sentence, "a man is  5 times as old as his son"

I will let X be the age of the old guy and Y be the age of his son:

{{{X = 5Y}}}

You can test that this equation is right, if his son was 1 years old, then the man would be 5 which is 5 times more then 1!

Continuing on with the second sentence

In 5 years he will be only 3 times as old as his son, find the present age?

If 5 years progress, both him and his son will have to add 5 years so:

{{{X + 5 = 3(Y + 5)}}}

To solve this equation, we know that {{{X = 5Y}}} so we plug in 5Y for every X.

{{{X + 5 = 3(Y + 5)}}} becomes
{{{5Y + 5 = 3(Y + 5)}}} Using distribution 
{{{5Y + 5 = 3Y + 15}}} Subtract 3Y on both sides and 5 on both sides
{{{2Y  = 10}}} Finally divide both sides by 2
{{{Y = 5}}}

Which says his son is 5 years old, how old is the man?

Go back to any equation, this will be easiest with this one:

{{{X = 5Y}}}
{{{X = 5*5}}}
{{{X = 25}}}

The man is 25 and his son is 5.