I assume you mean uniform distribution over .If each of them selects the time of arrival at random, what probability is it that the meeting will actually happen?"

Let be the time in hours after Noon that the first and the second person (resp) arrive.

You want to calculate

Break into 3 regions, because if then the lower/upper (resp.) bound on when is allowed to occur is bounded by 0/1 (resp.) rather than (resp.).

Seems to me like they out to work out a different scheme.