To express 0.8 as a fraction in simplest form, you can follow these steps:

Step 1: Write the decimal as a fraction by placing the decimal value over 1. In this case, it would be 0.8/1.

Step 2: Multiply both the numerator and denominator by 10 to remove the decimal. This gives you 8/10.

Step 3: Simplify the fraction by finding the greatest common divisor (GCD) of the numerator and denominator, which is 2 in this case. Divide both the numerator and denominator by the GCD to get the simplest form.

8 ÷ 2 / 10 ÷ 2 = 4/5

Therefore, 0.8 as a fraction in simplest form is 4/5.