OpenCourseWare on critical thinking, logic, and creativity

You're right!

Yes, this reasoning is correct. Superficially, this case resembles the prior two examples, but the difference here is that the chance of a bus coming in a given minute is not independent of what happened in the previous minutes, since the buses are timed to be a fixed number of minutes apart. When you first arrive at the bus stop, the bus has an equal chance of coming in each of the next 8 minutes, so the probability of it coming within one minute is 1/8. If it doesn't come in the first minute, then it must come in one of the following 7 minutes, so the probability of it coming within one minute goes up to 1/7. If it doesn't come in the first two minutes, the probability of it coming within one minute goes up to 1/6. And so on.

• Return to main text.

<< previous page