Name: Erin McKeon
Who is asking: Student
Level: Secondary

Question:
Why does the letter J represent the set of integers, the letter Q represent a set of rational numbers and the letter P represent a set of irrational numbers? What do each of these letters stand for?

The rationals are quotients of integers, and that is the reason for the letter Q to designate the rationals. The other letters you mention are not standard. I have seen J used for the integers but also I and, probably the most common, Z. I think that P for the irrationals is not at all common. The most common notation is to use R for the reals, Q for the rationals and then designate the irrationals R\Qor R-Q.