How many people are watching TV programme P?

A. Number of people watching TV programme Q is 1000 and number of  people watching both the programmes, P and Q, is 100.

B. Number of people watching either P or Q or both is 1500.

Considering 1st statement we know that number of people watching Q alone is 900 and both P and Q is 100. But we cant find the number of people watching P. Also, using statement B alone, we cannot find the number of people watching P. But if we consider B along with A , we can definately get total no. of people watching P . Hence, the question can be answered by using both the statements together, but cannot be answered by using either statement alone.