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15 Feb 2016, 21:28
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B
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
25%
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Question Stats:
78% (01:43) correct
22%
(02:24)
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The ratio of alcohol and water in three mixtures of alcohol and water is 3:2, 4:1, and 7:3. If equal quantities of the mixture are drawn and mixed, the concentration of alcohol in the resulting mixture will be?
A)65%
B)70%
C)75%
D)80%
Solution:
A)65%
B)70%
C)75%
D)80%
Solution:
With 3 quantities, the most straight forward method would be our usual weighted average formula.
We can use the scale method on two quantities at a time.
Here, I say that solution 1 has 3/5 alcohol and solution 2 has 4/5 alcohol. When we mix 1 part of each, we will get a mixture with 3.5/5 alcohol (it's simple average because both solutions are mixed in equal quantities).
3.5/5 = 7/10
Solution 3 has 7/10 alcohol.
2 parts of previous mix is mixed with 1 part of solution 3 but both have 7/10 alcohol. So the total mixture will have 7/10 = 70% alcohol.
Answer (B)
We can use the scale method on two quantities at a time.
Here, I say that solution 1 has 3/5 alcohol and solution 2 has 4/5 alcohol. When we mix 1 part of each, we will get a mixture with 3.5/5 alcohol (it's simple average because both solutions are mixed in equal quantities).
3.5/5 = 7/10
Solution 3 has 7/10 alcohol.
2 parts of previous mix is mixed with 1 part of solution 3 but both have 7/10 alcohol. So the total mixture will have 7/10 = 70% alcohol.
Answer (B)
15 Feb 2016, 22:12
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VeritasPrepKarishma
Quote:
The ratio of alcohol and water in three mixtures of alcohol and water is 3:2, 4:1, and 7:3. If equal quantities of the mixture are drawn and mixed, the concentration of alcohol in the resulting mixture will be?
A)65%
B)70%
C)75%
D)80%
how can the following problem be solved using the scale/ratio formula method?
A)65%
B)70%
C)75%
D)80%
how can the following problem be solved using the scale/ratio formula method?
The ratios are given such that the sum of alcohol and water can be brought up to 10 for each mixture. (Since equal quantities are to be added)
For 3:2 lets take 6 parts alcohol and 4 parts water
For 4:1 lets take 8 parts alcohol and 2 parts water
For last since the sum is already 10, 7 parts alcohol and 3 parts water.
Mixing these three will give 6+8+7 =21 units alcohol and 4+2+3=9 units water
or, 21 units alcohol in 30 units of mixture
21/30 *100 = 70%
Answer : B
General Discussion
powellmittra
Joined: 22 Dec 2015
Last visit: 31 Jan 2017
Posts: 29
Given Kudos: 366
Schools: ESMT"18 Mannheim"18 COpenhagen"18 HEC Montreal '19
20 May 2016, 09:54
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Concentration of Alcohol in 3 solutions are: 3/5, 4/5 and 7/10. Since equal parts are taken, let us assume 10 litres of each mixture was taken out. So,
Alcohol from Sol1 = 6
Alcohol from Sol2 = 8
Alcohol from Sol1 = 7
% of Alcohol in final solution = [(6 + 8 + 7)/30] * 100 = 70 %
Alcohol from Sol1 = 6
Alcohol from Sol2 = 8
Alcohol from Sol1 = 7
% of Alcohol in final solution = [(6 + 8 + 7)/30] * 100 = 70 %
