Seven friends M, N, O, P, Q, R and S, each has a different height. Only two people are taller than Q. P is taller than Q but shorter than O. M is taller than R but shorter than S. Only three people are taller than S. N is the shortest among all. The height of how many persons is between the heights of Q and R?

2

1: So first in the question, it is given that only two people are older than Q so the resulting framework will be 

- > -> Q >- > - >- >-

2: 5th line of the question states that only 3 people are younger than S so the resulting formation 

-> -> Q > S > - > - > -

3: Now please focus on two lines stating that P is older than Q but younger than O and M is older than R but younger than S and N is the youngest of all so the final formation will be 

O > P > Q > S > M > R >N 

So,  The age of two persons is between the ages of Q and R.