A doctor is visit to a patient. From the past experience, it is known that the probabilities that he will come by train, bus, scooter or by other means of transport, are respectively `3/10, 1/5,1/10` and `2/5` The probabilities that he will be late are `1/4,1/3` and `1/12` if he comes by train, bus and scooter respectively, but if he comes by other means of transport, then he will not be late. When he arrives, he is late. What is the probability that he comes by train?

Answer

`1/2`