There are 200 questions in the PMP exam and you have 4 hours. This means that you have 200 questions to finish in 240 minutes, which means that every question, on average, shouldn't take you more than 1.2 minutes, or 80 seconds.

Note: Although it is true that there are 25 non-scored (the so-called pretest) questions in the exam, you don't know which ones they are, so the 4 hours is attributed to all the 200 questions, and not just 175.