If the arithmetic mean of p and q is 10 and the arithmetic mean of q and r is 20, what is the value of r-p? Choose the correct choice from the following answers
A) 20
B) 10
C) 30
D) 40
E) 5
20rithmetic mean expression for p and q:   (p+q)/2=10 ; p+q=20 ----eq1   20rithmetic mean expression for q and r:   (q+r)/2=20 ; q+r=40 ----eq2   Subtracting eq1 from eq2 we get: r-p=20   Hence, the correct answer is 20
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If the arithmetic mean of p and q is 10 and the arithmetic mean of q and r is 20, what is the value of r-p?