Answer:
4/5 or 80% or 0.8 (depending on format)
Explanation:
There are 5 possibilities that it could do; land on a 1, land on a 2, land on a 3, land on a 4, and land on a 5. The probability of it not landing on a four would be the probability of landing on a 1, 2, 3, or 5 (1/5+1/5+1/5+1/5). 1/5+1/5+1/5+1/5 = 4/5