Just divide.
[tex]\sf\dfrac{7}{12}\rightarrow7\div12\rightarrow0.58\overline{3}[/tex]
0.583333. . .
^ This is the thousandths place
Look at the number after that, if it's 5 or more we round up, if it's 4 or less we round down.
It's 3, so we round down to 0.583.
