A candidate takes three tests in succession and the probability of passing the first test is . The…

A candidate takes three tests in succession and the probability of passing the first test is $\frac{1}{2}$. The probability of passing each succeeding test is $\frac{1}{2}$ or $\frac{1}{4}$ depending on whether he passes or fails in the preceding one. The candidate is selected, if he passes at least two tests. Find the probability that the candidate is selected.