A sample space S consists of three mutually exclusive and exhaustive events E₁, E₂ and E₃. A student assigns probabilities P(E₁)=0.3, P(E₂)=0.5 and P(E₃)=0.4. Determine the validity of this assignment.
a) Valid because the probabilities satisfy P(E1)+P(E2)+P(E3)=1.
b) Invalid because the probabilities sum to a value greater than 1.
c) Valid because all probabilities are non-negative.
d) Invalid because one of the probabilities exceeds 0.5, which is not allowed for three events.