What is the probability that a number selected from numbers 1, 2, 3, ......, 30, is prime number, when each of the given numbers is equally likely to be selected?

Answer: Option C

X = {2, 3, 5, 7, 11, 13, 17, 19, 23, 29}
n(X) = 10, n(S) = 30
Hence required probability,
$$\begin{array}{rl}& =\frac{n(X)}{n(S)}\\ & =\frac{10}{30}\end{array}$$