To convert the decimal 0.8 to a rational number, you can express it as a fraction.
0.8 can be written as:
\[ 0.8 = \frac{8}{10} \]
Next, you can simplify this fraction. Both the numerator and the denominator can be divided by their greatest common divisor, which is 2:
\[ \frac{8 \div 2}{10 \div 2} = \frac{4}{5} \]
Thus, the decimal 0.8 as a rational number is \(\frac{4}{5}\).