Quantitative Aptitude Ques 778

Question: A container contains a mixture of two liquids A and B in the ratio of 7: 5. When 9 L of mixture is drawn off and the container is filled with B, the ratio of A and B becomes 7: 9. How many litres of liquid A was contained by the container initially?

Options:

A) 10

B) 20

C) 21

D) 25

Show Answer

Answer:

Correct Answer: C

Solution:

  • Suppose the container initially contains $ 7x $ and $ 5xL $ of mixtures A and B, respectively. Quantity of A in mixture left' $ =( 7x-\frac{7}{12}\times 9 )=( 7x-\frac{21}{4} )L $ Quantity of B in mixture left $ =( 5x-\frac{5}{12}\times 9 )=( 5x-\frac{15}{4} )L $

$ \therefore $ $ \frac{( 7x-\frac{21}{4} )}{( 5x-\frac{15}{4} )+9}=\frac{7}{9} $

$ \Rightarrow $ $ \frac{28x-21}{20x+21}=\frac{7}{9} $

$ \Rightarrow $ $ 252x-189=140x+147 $

$ \Rightarrow $ $ 112x=336 $

$ \Rightarrow $ $ x=3 $

$ \therefore $ Quantity of liquid A in the container $ 7\times 3=21L $

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