smackmartine wrote:Posting the correct question... Some people don't even care to edit the wrong question!!!
10 kg of soil mixture X consists of 30% of sand and 70% of clay. By replacing how many kiligrams of soil with the same kilograms of pure sand, the new soil will consist of 50 percent of sand?
a. 7/5
b. 5/7
c. 20/7
d. 10/7
e. 20/3
Percentage of sand in X = 30.
Percentage of sand in the pure sand = 100.
Percentage of sand in the mixture = 50.
We can use alligation to determine the ratio of the elements in the mixture.
Alligation dictates the following:
The proportion of each element in the mixture = the distance between the percentage attributed to the other element in the mixture and the percentage attributed to the mixture.
Thus:
Proportion of X in the mixture = |100-50| = 50.
Proportion of sand in the mixture = |30-50| = 20.
X : Sand = 50:20 = 5:2.
Thus, for every 5+2=7 grams of mixture, 2 grams must be pure sand. In other words, the pure sand must be 2/7 of the mixture.
(2/7)*10 = 20/7.
The correct answer is
C.
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