Given:
[tex]\text{Let x=0.7999}\ldots\text{ (1)}[/tex]Multiply euation (1) by 10 on both sides
[tex]10x=7.999\ldots\text{ (2)}[/tex]Multiply equation (1) by 100 on both sides
[tex]100x=79.999\ldots\text{ (3)}[/tex]Subtract equation(2) from equation(3)
[tex]90x=72[/tex][tex]x=\frac{72}{90}[/tex][tex]x=\frac{4}{5}[/tex][tex]0.79=\frac{4}{5}[/tex]