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 is equal to one of the numbers 5/11 , 7/12 , 9/13 , what is the value of a?
1. 5/11 < a < 3/4
2. 11/13 > a > 1/2
In the original condition there is 1 variable (a) and thus we need 1 equation to match the number of variable and equation. Since there is 1 each in 1) and 2), D has high probability of being the answer.
1) a=7/12, 9/13 noy suffi because not unique
2) a=7/12, 9/13 noy suffi because not unique
1) & 2) a=7/12, 9/13 noy suffi because not unique. therefore the answer is E
Normally for comparing fractions, we use cross methods. In other words, 5/11<7/12 --> cross-multiplying leads to 5*12<7*11 therefore the inequality sign is correct. Same goes for 9/13<3/4 --> 9*4<13*3
Normally for cases where we need 1 more equation, such as original conditions with 1 variable, or 2 variables and 1 equation, or 3 variables and 2 equations, we have 1 equation each in both 1) and 2). Therefore D has a high chance of being the answer, which is why we attempt to solve the question using 1) and 2) separately. Here, there is 59 % chance that D is the answer, while A or B has 38% chance. There is 3% chance that C or E is the answer for the case. Since D is most likely to be the answer according to DS definition, we solve the question assuming D would be our answer hence using 1) and 2) separately. Obviously there may be cases where the answer is A, B, C or E.
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