40% of a 70% vinegar solution is replaced with water. From the resulting solution, again 10% is replaced with water. This step is repeated once more. What is the concentration of vinegar in the final solution obtained?  Choose the correct choice from the following answers:  A) 34%  B) 23%  C) 42%  D) 28%  E) 37%
A quick answer: (70)(0.6)(0.9)(0.9)   Imagine you have 100 ml of 70% vinegar solution.   In step 1, 40% of the vinegar solution is replaced with water. This means 60% of the original vinegar quantity remains. Hence the resultant concentration is (70)(0.6) = 42%   Next, 10% of this solution is replaced with water and the process is repeated. Both the times, 90% of the previous vinegar quantity remains. Thus, 42x0.9x0.9 = 34%   This gives the final concentration as 70x0.6x0.9x0.9 = 34%   34%nswer: 34%
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40% of a 70% vinegar solution is replaced with water. From the resulting solution, again 10% is replaced with water. This step is repeated once more. What is the concentration of vinegar in the final solution obtained?