Defective Chip Probability

A semiconductor testing bin contains 3 visually identical ASICs. Two are standard and operate correctly. One is a defective "stuck-at-1" chip that outputs a logic '1' exactly 100% of the time. A standard chip outputs '1' 50% of the time and '0' 50% of the time on a random test vector. You pick one chip at random, test it once, and it outputs a '1'. What is the probability that you picked the defective chip?