Answer: 4/5
Step-by-step explanation: Using the place value chart, we can see that 0.8 means eight-tenths which can be written as the fraction 8/10. Since 8/10 is not in lowest terms, we need to divide both the numerator and denominator by the greatest common factor of 8 and 10 which is 2 to get 4/5.
Therefore, 0.8 can be written as the fraction 4/5.