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.

How many people are standing in line?

(1) Three people are standing in front of Alan and three people are standing behind David.

(2) Two people are standing between Alan and David.

In the original condition, because we have to know the number of “key” people in line, there are numerous variables. In order to match the number of variables and the number of equations, we need numerous equations as well. Since both the condition 1) and 2) has 1 equation, there is high chance E is the answer.

Using both the condition 1) and 2), we cannot know who is in front between David and Alan. 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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