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.
At a certain wedding, the bar served only beer and wine. If 320 people attended the wedding and 200 attendees drank wine, how many attendees drank neither beer nor wine?
(1) There were the same number of beer drinkers as nondrinkers.
(2) The same number of people drank only beer as drank both beer and wine
Transforming the original condition and the question, we have 2by2 question and below table.
We have 4 variables (a,b,c,d) and 2 equations (a+b+c+d=320, a+b=20) in the table. In order to match the number of variables and equations, we need 2 more equations and since there is 1 each in 1) and 2), C has high probability of being the answer. It turns out that C actually is the answer.
Normally for cases where we need 2 more equations, such as original conditions with 2 variable, or 3 variables and 1 equation, or 4 variables and 2 equations, we have 1 equation each in both 1) and 2). Therefore C has a high chance of being the answer, which is why we attempt to solve the question using 1) and 2) together. Here, there is 70% chance that C is the answer, while E has 25% chance. These two are the key questions. In case of common mistake type 3,4, the answer may be from A, B or D but there is only 5% chance. Since C is most likely to be the answer according to DS definition, we solve the question assuming C would be our answer hence using ) and 2) together. (It saves us time). Obviously there may be cases where the answer is A, B, D or E.
Attachments
GCDS shasadou At a certain wedding(20150916).jpg [ 20.9 KiB | Viewed 4131 times ]
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