VeritasPrepKarishma wrote:
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?
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)
ALTERNATE APPROACH
Let the composition of mixtures be -
A = Alcohol (30) Water (20) { RATIO IS 3:2}
B = Alcohol (40) Water (10) { RATIO IS 4:1}
C = Alcohol (35) Water (15) { RATIO IS 7:3}
Quote:
if equal quantities of the mixture are drawn and mixed
Let 10 units is drawn -
A = Alcohol (6) Water (4) { RATIO IS 3:2}
B = Alcohol (8) Water (2) { RATIO IS 4:1}
C = Alcohol (7) Water (3) { RATIO IS 7:3}
Total alcohol = 21 and water = 9
Net concentration of alcohol is 21/30*100 =>70%
Answer will be (B)
_________________
Thanks and Regards
Abhishek....
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76% (01:44) correct 
