Question 27682
Let the age of Mrs. Jones be y. Let the age of her son be x.


Mrs. Jones is three times as old as her son:
{{{y=3x}}}


Ten years ago, she was 5 times as old as her son was then:
{{{y-10=5(x-10)}}}
{{{y-10=5x-50}}} (Expand the brackets)
{{{y=5x-40}}} (Add 10 on both sides)


Now, you can compare the first equation with the second equation.
{{{3x=5x-40}}}
{{{2x=40}}} (Group {{{3x}}} and {{{5x}}} together)
{{{x=20}}} (Age of her son)


Her son is 20 years old.