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

Answer

`(1)/(2)`