Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.
A candy wholesaler needs to quickly sell some candy bars that are nearing their expiration date, so he reduced the price of the candy bars. By what percent did he reduce the price of the candy bars?
(1) The price of a candy bar was reduced by 36 cents.
(2) If a candy retailer purchases a case of 144 candy bars from the wholesaler, she will save $51.84 as a result of the price reduction.
There are 3 variables (n: the number of the candy bars sold, p: the original price of the candy bars and r: the reduced price of the candy bars) in the original condition. In order to match the number of variables and the number of equations, we need 3 equations. Since the condition 1) and 2) each has 1 equation, there is high chance E is the answer.
Using the both condition 1) and 2), we obtain p-r=0.36 and 144(p-r)=51.84. However, we cannot know the total number of the candy bars purchased. Therefore, the correct answer is E.
For cases where we need 3 more equations, such as original conditions with “3 variables”, or “4 variables and 1 equation”, or “5 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 80% chance that E is the answer (especially about 90% of 2 by 2 questions where there are more than 3 variables), while C has 15% chance. These two are the majority. In case of common mistake type 3,4, the answer may be from A, B or D but there is only 5% chance. Since E is most likely to be the answer using 1) and 2) separately according to DS definition (It saves us time). Obviously, there may be cases where the answer is A, B, C or D.
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