Let [tex]x[/tex] be John's age today. Five years ago, John's age was [tex]x -5[/tex].
In eight years, John's age will be [tex]x+8[/tex].
Therefore, the statement "5 years ago John's age was half of the age he will be in 8 years" written in symbols is:
[tex]x- 5 = \frac{1}{2} (x+8)[/tex].
Multiplying both sides by [tex]2[/tex], we have [tex]2x-10 = x+8[/tex]
which gives [tex]x = 18[/tex].
Therefore, John is 18 years old today.
