If f = 3r(s/1000)^2 and s = 2000, what is r in terms of f ?

Question

If  f = 3r(\frac{s}{1000})^2  and  s = 2000 , what is  r  in terms of  f ?

(A)  \frac{f}{6}

(B)  \frac{f}{12}

(C)  \frac{f}{36}

(D)  \frac{f^2}{36}

(E)  \frac{3f}{4}

Bunuel · Answer

Substituting  s = 2000  into  f = 3r(\frac{s}{1000})^2  we get:

f = 3r(\frac{2000}{1000})^2

f = 3r(2)^2

f = 12r

r=\frac{f}{12}  
 
Answer: B.

DanTheGMATMan · Answer

Substitute in for S. Solve for R

https://www.youtube.com/watch?v=J2xAygkIRKs

GMATinsight · Answer

Just substitute s = 2000 in primary expression

s/1000 = 2000/1000 = 2

f = 3r(\frac{s}{1000})^2  
 f = 3r(\frac{2000}{1000})^2  
 f = 3r(2)^2 
 f = 12r 
 \frac{f}{12} = r

Answer: Option B

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