A solution of X pounds of water and sugar is boiled until 20% of the water content evaporates. Originally q% of sugar was present in the solution. After evaporation, what percentage of the solution is sugar? Choose the correct choice:
A) 100q/(1-q)	B) 80q/(1-q)	C) 75q/(1-q)	D) 100q/(80-0.2q)	E) 100q/(80+0.2q)
We'll go for the ALTERNATIVE approach since there are variables in all the answers (which means that any number could work). Since the question deals with percents, the easiest number to use is X = 100. Now let's say that q = 10. Before the evaporation we had 10 pound of sugar and 90 pounds of water. Since only water evaporated, after the evaporation the 10 pounds of sugar remained the same, but the water reduced by 20% of 90 (18 pounds), so we have only 72 pounds of water. 10 out of 82 is the fraction of sugar, so if we multiply it by 100 we get the percents. The correct answer is 100q/(80+0.2q): 100q/(80+0.2q) &gt;&gt;&gt; 100x10 / 82
<result>E</result>
A solution of X pounds of water and sugar is boiled until 20% of the water content evaporates. Originally q% of sugar was present in the solution. After evaporation, what percentage of the solution is sugar?