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15 Feb 2016, 21:28
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B
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79% (01:44) correct
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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
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
20 May 2016, 13:13
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You just have to sum the ratios, and then you'll have 14:6 which equals 7:3, so you have 7 parts alcohol for every 3 of water (70%).
