The fraction form for 50% is :
[tex] \frac{50}{100} [/tex]
Now do the multiplication you will get :
[tex] \frac{50}{100} \times \frac{1}{3} = \frac{50}{300} [/tex]
Next step is to simplify the fraction :
[tex] \frac{50}{300} = \frac{1}{6} [/tex]
This is the simplest form of the fraction.
Hope this helps you :)