20% of an 30% salt solution is replaced with water. From the resulting solution, again 20% is replaced with water. This step is repeated once more. What is the concentration of salt in the final solution obtained  Choices:
A) 19.58%
B) 15.36%
C) 20%
D) 9.72%
E) 11.64%
A quick answer: (30)(0.8)(0.8)(0.8)   Imagine you have 100 ml of 30% salt solution.   In step 1, 20% of the salt solution is replaced with water. This means 80% of the original salt quantity remains. Hence the resultant concentration is (30)(0.8)   This process is repeated for step 2 and three. Hence, we multiply 30 ml two more times with 0.8.   This gives the final concentration as 30x0.8x0.8x0.8 = 15.36%   Answer: 15.36%
<result>B</result>
20% of an 30% salt solution is replaced with water. From the resulting solution, again 20% is replaced with water. This step is repeated once more. What is the concentration of salt in the final solution obtained