Originally Posted by

**awkward** ohwcomp,

You have correctly guessed (I think) that the author of Q2 expects you to say the distribution of the number of cars is Poisson.

[grump] However, in my role as curmudgeon, I wish to state that there is nothing in the problem statement to support this-- it's just a hopeful assumption. Mathematicians find it convenient to assume a Poisson distribution (and exponential inter-arrival times), because these distributions lend themselves to analytical solutions. Sometimes the convenience overrides real-world considerations. In my personal experience cars in traffic often arrive in batches, but that isn't the way a Poisson distribution behaves. [/grump]