alphonsa wrote:
Fresh grapes contain 80% water by weight and raisins obtained by drying fresh grapes contain 25% water by weight. How many kgs of fresh grapes are needed to get 20kgs of raisins?
A) 75 kgs
B) 64kgs
C) 72 kgs
D) 65 kgs
E) 70 kgs
Source: 4gmat
Please explain
Let x = the number of kilograms of fresh grapes needed to obtain 20 kgs of raisins.
The amount of non-water material in x kgs of fresh grapes is 0.2x. The amount of non-water material in 20 kgs of raisins is 0.75*20 = (3/4)*20 = 15. Since the non-water material remains constant after drying fresh grapes to obtain raisins, we can create the following equation:
0.2x = 15
2x = 150
x = 75
Therefore, 75 kilograms of fresh grapes are needed in order to obtain 20 kgs of raisins after drying.
Answer: A
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