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.

Ann deposited money into two new accounts, A and B. Account A earns 5 percent simple annual interest and account B earns 8 percent simple annual interest. If there were no other transactions in the two accounts, then the amount of interest that account B earned in the first year was how many dollars greater than the amount of interest that account A earned in the first year?

(1) Ann deposited $200 more in account B than in account A.

(2) The total amount of interest that the two accounts earned in the first year was $120.

There are 3 variables (original money, interest rate, time period) in questions regarding compound and and simple accounts

For this question above, the time period is told to be 1 year, and the interest rates are told to be 5% and 8% respectively, so we only need to know the original money, which means there are 2 variables (A,B) and 2 equations are given by the 2 conditions, so there is high chance (C) will become the answer.

Looking at the conditions together, from B=A+200, A*5%+B*8%=120, we can derive an unique answer for the interests, so the conditions are sufficient and the answer becomes (C).

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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