If we want the probability of Fiona waking up before 8am for at least one of the days, we can calculate the probability of she not waking up 8am in both days, and then we do 1 minus this probability.
The probability of she not waking up 8am in one day is (1 - 2/5) = 3/5
The probability of she not waking up 8am in both days is 3/5 * 3/5 = 9/25
So, the probability of Fiona waking up before 8am for at least one of the days is (1 - 9/25) = 16/25 = 0.64 = 64%
of rice