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.

If production on line A increased 5% from 2006 to 2007, and if production on line B increased 10% in the same period, how many units did line A produce in 2006?

(1) The two lines combined produced 100,000 units in 2006.

(2) The two lines combined produced 107,500 units total in 2007.

From the original condition and the question, we can obtain the below 2by2 table that is common in GMAT math test

Attachment:

GCDS Bunuel If production on line A(20151007).jpg [ 23.25 KiB | Viewed 1331 times ]
In the above table, we have 2 variables (A,B), and 2 equations given from the 2 conditions, making it likely that (C) is going to be our answer as the number of variables and equations match;

Looking at the conditions together,

A+B=100,000

1.05A+1.1B=107,500.

The conditions are sufficient to solve for the variables, and the answer actually is (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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