Bunuel wrote:

tonebeeze wrote:

I got this problem correct during the test by plugging in values and testing. I would like to learn the algebra. Please advise. Thanks.

Gold depreciated at a rate of \(X%\) per year between 2000 and 2005. If 1 kg of gold cost \(S\) dollars in 2001 and \(T\) dollars in 2003, how much did it cost in 2002?

a. \(T\frac {S}{2}\)

b. \(T\sqrt{\frac{T}{S}}\)

c. \(T\sqrt{S}\)

d. \(T\frac{S}{\sqrt {T}}\)

e. \(\sqrt{ST}\)

Price of 1kg gold in 2001 - \(S\);

Price of 1kg gold in 2002 - \(S(1-\frac{x}{100})\);

Price of 1kg gold in 2003 - \(S(1-\frac{x}{100})^2=T\) --> \((1-\frac{x}{100})=\sqrt{\frac{T}{S}}\);

Price of 1kg gold in 2002 - \(S(1-\frac{x}{100})=S*\sqrt{\frac{T}{S}}=\sqrt{ST}\).

Answer: E.

Thank you for posting and including into GMAT Club free test.

I find the phrasing of the question obscure: all three parameters (i.e. S, T and X%) are included as known parameters.

But then the question asks to express 2002 value in terms of S and T (and not X%) which only becomes clear when you look at the answers.

I suggest the following rephrasing: "how much did it cost in 2002 in terms of S and T?"