[tex]\frac{12}{100}=0.12[/tex]
To get the 0.12 to repeat, the trick is to subtract 1 from the denominator
[tex]\frac{12}{99}=0.12121212...[/tex]
Then reduce the fraction.
[tex]\frac{12}{99}={4}{33}[/tex]
now add the 3 to get
[tex]3.12121212.... = 3\frac{4}{33}[/tex]
