A circular spinner has four numbers (10,20,30 and 40) marked on it. If the spinner is rolled, the value indicated by the pointer is a random variable X.

A student investigated the spinner and claimed that the probability distribution of X is given below:

x 10 20 30 40
P(x = x) 1/8 1/3 1/4 3/8

Justify if the distribution claimed by the student is possible and give one reason to support your answer.