Finding Positive Integers for Irrational Number Interval

[TJK]

someome please help me with this problem:
"Any real numbers x and y with 0 < x < y, there exist positive integers p
and q such that the irrational number s =( p√2)/q is in the interval (x; y)."

 

[micromass]

Do you know that the rationals are dense in the reals?? What does that mean??