QA – Placement Quizzes | Mixtures and Alligation | Question 13

A drum filled with a mixture of two liquids l1 and l2 in the ratio 5:7. When 9 liters of mixture is taken out and the replaced by l1. Now the ratio of l1 and l2 is 9:7. How many liters of the liquid l1 were there in the drum initially?
(A) 15
(B) 20
(C) 18
(D) 25


Answer: (A)

Explanation: Let the initial quantity of l1 in the container be 5x.
Let the initial quantity of l2 in the container be 7x.
Now, 9 liters of mixture is drawn off from the container.
Quantity of l1 in 9 liters of the mixture drawn off
=9*5/12=15/4
Quantity of l2 in 9 liters of the mixture drawn off
=9*7/12=21/4
Hence,
Quantity of l1 remaining in the mixture after 9 liters is drawn off
=5x−15/4
Quantity of l2 remaining in the mixture after 9 liters is drawn off
=7x−21/4
Since the container is filled with l1 after 9 liters of mixture is drawn off, quantity of l1 in the mixture
=5x-15/4+9=5x+21/4.

Given that the ratio of l1 and l2 becomes 9:7
⇒5x+21/4:7x-21/4=9:7
⇒20x+21:28x-21=9:7
⇒7(20x+21)=9(28x-21)
⇒140x+147=252x-189
⇒112x=336
⇒x=3.

Therefore, liters of l1 present in the container initially
=5x=(5*3)=15.

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