In a certain town, 10% of people commute to work by bicycle. If a person is selected randomly from the town, what are the odds against selecting someone who commutes by bicycle?

odds in against an event is ratio of probability of complement of an event to its probability, i.e., $\setminus \frac{1 - 0.1}{0.1} = \frac{9}{1} = 9 : 1$