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.

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The figure above shows a construction plan for the intersection of three straight roads, each having parallel edges and each having the same width. what is the value of t?

(1) r = 140

(2) s = 160

From the original condition, we can see that there are 3 variables (r,s,t), and one equation (r+s+t=360), so we need 2 more equations, which are given from the 2 conditions, so there is high chance (C) will be our answer.

Looking at the conditions together, r+s+t=140+160+t=360, so it answers the question 'yes', and the answer becomes (C).

For cases where we need 2 more equation, such as original conditions with “2 variables”, or “3 variables and 1 equation”, or “4 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 70% chance that C is the answer, while E has 25% 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 C 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, D or E.

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