A compay has two plants to manufacture bicycles. Plant I manufacture 70% of the bicycles and plant II manufacture 30%. At plant I, 80% of the bicycles are rated as of standard quality and a plant II , 90% of the bicycles are rated as of standard quality. A bicycle is choosen at random and is found to be of standard quality. What is the probability that it has come from plant II. Which mode of conveyance preferred by you at the most? why?