Suppose a uniform random variable can be used to describe the outcome of an experiment with the outcomes ranging from 30 to 70. What is the probability that this experiment results in an outcome less than 40? ... ?

Lets part from saying that the probability of obtaining any one of these scores is: P = 140 Since each of these events is mutually exclusive, the probability of obtaining a score less than 40 is:

P (X<40) = P (X = 1/30 ∪ 1/31 ∪ ... ∪ 1/39) = P (1/30) + P (1/31) + ... + P (1/39) = 1/40 + 1/40 + ... + 1/40 = 9/40