Could you please explain #38 of practice test 9?


Sure! This is a percent change question, so the formula you need to know is:

\text{Percent Change}=\dfrac{\text{Final Amount} - \text{Starting Amount}}{\text{Starting Amount}}\times 100\%.

From the table, we know that there were 24.7 million international tourist arrivals in Russia in 2012, and that this was 13.5% greater than the 2011 number. We’re asked for the difference between the 2011 number and the 2012 number, to the nearest integer. Therefore, we drop the 2012 number as the Final Amount and the percent change into the formula and solve. We’ll use x for the 2011 number.

\text{Percent Change}=\dfrac{\text{Final Amount} - \text{Starting Amount}}{\text{Starting Amount}}\times 100\%\\\\13.5\%=\dfrac{24.7-x}{x}\times 100\%\\\\0.135=\dfrac{24.7-x}{x}\\0.135x=24.7-x\\1.135x=24.7\\x\approx 21.8

But be careful! The question isn’t asking you for the 2011 number. It’s asking for the difference between 2012 and 2011! So as a last step we have to subtract and then round to the nearest integer.

24.7-21.8\approx 3

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