Official Solution: Charlie invested \($x\) in Fund A for one year at an annual simple interest rate of \(p\) percent. What would be the total value of this investment at the end of that period? This is a fairly straightforward question, but some might fall into the C-trap or mistakenly choose D as the answer.
Essentially, we need to find the value of \(x(1 + \frac{p}{100})\).
(1) If Charlie had invested twice as much money in Fund A, the total value of the investment would have been $220 at the end of the year.
This implies that \((2x)(1 + \frac{p}{100}) = 220\), which, by dividing by 2, yields \(x(1 + \frac{p}{100}) = 110\). This is exactly what we want to find. Sufficient.
Or, by simple reasoning, if doubling the initial investment amounts to $220 in one year, the initial investment will amount to half of that, so $110.
(2) If Charlie had invested at twice the percentage in Fund A, the total value of the investment would have been $120 at the end of the year.
This implies that \(x(1 + \frac{2p}{100}) = 120\), which cannot be simplified to get the value of \(x(1 + \frac{p}{100})\) nor can it be solved to get the individual values of \(x\) and \(p\) to calculate \(x(1 + \frac{p}{100})\). Not sufficient.
Answer: A