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.
To fill an order, a manufacturer had to produce 1000 tools per day for n days. what is the value of n?
(1) Because of production problems, the manufacturer produced only 600 tools per day during the first 5 days
(2) Because of production problems, the manufacturer had to produce 1,500 tools per day on each of the last 4 days in order to meet the schedule
In the original condition, there are 2 variables(power, n), which should match with the number of equations. So you need 2 equations. For 1) 1 equation, for 2) 1 equation, which is likely to make C the answer. When 1) & 2),
Since the manufacturer produced 600 tools every day for the first 5 days, they produced 3000 tools. Then the manufacturer produced 6000 tools for the next 4 days and you don’t know n. So, value of n is not unique and not sufficient. Therefore, the answer is E.
-> For cases where we need 2 more equations, 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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