Determine, with justification, whether each of the following sets is finite, countably infinite, or uncountable.

a) { $\displaystyle x \in Q | 1 < x < 2 $ }

b) { $\displaystyle m/n | m, n \in N, m < 100, 5 < n < 105 $ }

I am lost. Not sure how to approach these problems!

Thanks.