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21 Mar 2020, 20:27
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D
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
25%
(medium)
Question Stats:
80% (01:54) correct
20%
(02:26)
wrong
based on 173
sessions
History
Date
Time
Result
Not Attempted Yet
A sample of 20 gallons of gasoline is found to be adulterated to the extent of 15%. How much pure gasoline should be added to bring up the level of purity to 95%?
A. 20
B. 25
C. 30
D. 40
E. 45
A. 20
B. 25
C. 30
D. 40
E. 45
Let the given solution of 20 gallons of gasoline with 15% adulteration be
Solution A
i.e. solution A has 85% pure gasoline
Let the solution of x gallons of pure gasoline to be added to bring up the level of purity be
Solution B
i.e. solution B has 100% pure gasoline
Now, to create resultant solution with 95% purity,
subtracting the %'s of pure gasoline and assigning the resultant absolute difference to the opposite solutions -
(solution A: 85% pure gasoline) - (resultant solution with 95% purity)
i.e. (85 - 95) = 10
assigning this value to solution B
(solution B: 100% pure gasoline) - (resultant solution with 95% purity)
i.e. (100 - 95) = 5
assigning this value to solution A
solution A : solution B
a ratio of 5 : 10
i.e. a ratio of 1 : 2
Thus, we need a 1:2 ratio of solution A : solution B to get the required 95% level of purity.
Thus, 2x20 = 40 gallons of solution B i.e. pure gasoline needs to be added.
Now when we are 40 gallons of pure gasoline (solution B) to 20 gallons of 15% adulterated solution, we have -
40+17 = 57 gallons of pure gasoline out of 60 gallons of resulting solution
which is what we require, 95% level of purity
Hence, Answer option D is correct.
Solution A
i.e. solution A has 85% pure gasoline
Let the solution of x gallons of pure gasoline to be added to bring up the level of purity be
Solution B
i.e. solution B has 100% pure gasoline
Now, to create resultant solution with 95% purity,
subtracting the %'s of pure gasoline and assigning the resultant absolute difference to the opposite solutions -
(solution A: 85% pure gasoline) - (resultant solution with 95% purity)
i.e. (85 - 95) = 10
assigning this value to solution B
(solution B: 100% pure gasoline) - (resultant solution with 95% purity)
i.e. (100 - 95) = 5
assigning this value to solution A
solution A : solution B
a ratio of 5 : 10
i.e. a ratio of 1 : 2
Thus, we need a 1:2 ratio of solution A : solution B to get the required 95% level of purity.
Thus, 2x20 = 40 gallons of solution B i.e. pure gasoline needs to be added.
Now when we are 40 gallons of pure gasoline (solution B) to 20 gallons of 15% adulterated solution, we have -
40+17 = 57 gallons of pure gasoline out of 60 gallons of resulting solution
which is what we require, 95% level of purity
Hence, Answer option D is correct.
21 Mar 2020, 22:47
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I got the wrong answer because I missed the inference of key points. i spent more time to understand and get it right.
if the sample is 15% adulterated, all the 20 gallons are adulterated in the same percentage. 15% of 20 gallons = 3 gallons.
to bring the purity to 95%, the percentage of adulteration should be reduced to 5%.
3 gallons is 5% of 60 gallons. to bring the existing volume of 20 gallons to 60 gallons, we have to add 60 - 20 = 40 gallons of gasoline.
answer is D.
cheers
if the sample is 15% adulterated, all the 20 gallons are adulterated in the same percentage. 15% of 20 gallons = 3 gallons.
to bring the purity to 95%, the percentage of adulteration should be reduced to 5%.
3 gallons is 5% of 60 gallons. to bring the existing volume of 20 gallons to 60 gallons, we have to add 60 - 20 = 40 gallons of gasoline.
answer is D.
cheers
