A Population Survey

The primer question influences people's views of what sort of size population the Philippines is likely to have.  Asking whether people believe it is more than 30 million suggests that the correct answer is about 30 million, so it is likely that people will estimate an answer close to 30 million, and similarly for the 70 million question. 

It is also likely to be the case that the spread of estimates will be much smaller with the primer question than without it.  Whether this is the case or not will become clear over time as more people respond to the survey!

If we want to know people's "genuine" views or ideas, then, we must be very careful not to ask primer questions beforehand.  Any question which hints towards a certain type of response might well influence the results of later questions.

On the other hand, primer questions can be very desirable if the survey's actual purpose is to influence people.  For example, if ACME Widgets wanted to influence people to shop in its stores, it could send out people to do surveys on a high street, asking them questions such as, "Which of the following would you be most likely to visit ACME Widgets to buy?  (A) ..., (B) ..., (C) ..., (D) something else" before asking them "Which store are you most likely to visit to buy X?"  This is quite obvious, though, and people might well realise that it's a marketing ploy, so the primer question may be more subtle than this.  However, it is important to be aware that this sort of survey is not actually a survey but a marketing tool, and there are laws relating to marketing which must be followed in such a case.