Find the value of

Which is the property that is there in the set of all rationals but not in the set of all integers?

What is the value of

Find all rational numbers each of which is equal to its reciprocal.

A bus shuttles between two neigbouring towns every two hours. It starts from 8 AM in the morning and the last trip is at 6 PM. On one day the driver observed that the first trip had 30 passengers and each subsequent trip had one passenger less than the previous trip. How many passengers travelled on that day?