On January 1, 2010, David invests 40% of his retirement savings in Antarctic largecap stocks, 20% in Antarctic midcaps, and 40% in Antarctic smallcaps. In 2010, largecaps rise 10%, midcaps rise 20%, and smallcaps rise 5% in the Antarctic stock market; however, in 2011, largecaps fall 5% and midcaps fall 10%, while smallcaps rise x% in Antarctica. If, on January 1, 2012, David has the same total amount of retirement savings as he did two years before, then x is between  Select.
A) 0 and 5 B) 5 and 10 C) 10 and 15 D) 15 and 20 E) 20 and 25
Pick a smart number for the total retirement savings David starts with—say, $10,000. (If you pick $100, you’ll wind up needing to track decimals, so give yourself more zeros to start with.)   Here are the starting values:   L = $4000   M = $2000   S = $4000   Apply the first year’s changes, so that you have these numbers on 1/1/2012:   Newer L = $4000+ 10% = $4400   Newer M = $2000 + 20% = $2400   Newer S = $4000 + 5% = $4200   Now apply the second year’s changes to L and M:   Newest L = $4400– 5% = $4400– $220 = $4180   Newest M = $2400– 10% = $2400– $240 = $2160   Add these to get $6340. So the newest S must be $10,000 (the target final total of David ’s retirement savings) minus $6340, $3660   The dollar change in S from 1/1/12 to 1/1/13 is $4200 – $540 = $3660. So the question is this: what percent change does $540 represent, from a starting point of $4200? Since $4200 is a nasty divisor, switch to benchmarks:   5% of $4200 = $210.   So 10% is just double that, or $420.   15% is $630.   And so on.   From this $540 lies between $420and $630   The correct answer is 10 and 15.
<result>C</result>
On January 1, 2010, David invests 40% of his retirement savings in Antarctic largecap stocks, 20% in Antarctic midcaps, and 40% in Antarctic smallcaps. In 2010, largecaps rise 10%, midcaps rise 20%, and smallcaps rise 5% in the Antarctic stock market; however, in 2011, largecaps fall 5% and midcaps fall 10%, while smallcaps rise x% in Antarctica. If, on January 1, 2012, David has the same total amount of retirement savings as he did two years before, then x is between