A container contains a mixture of two liquids P and Q in the ratio 7 : 5. When 9 litres of mixture are
drawn off and the container is filled with Q, the ratio of P and Q becomes 7 : 9. How many litres of liquid
P was contained in the container initially?
Pick one:
A) 23
B) 21
C) 19
D) 17
E) 18
Explanation :   Let's initial quantity of P in the container be 7x and initial quantity of Q in the container be 5xNow 9   litres of mixture are drawn off from the containerQuantity of P in 9 litres of the mixtures drawn off =   9×712=6312=214Quantity of Q in 9 litres of the mixtures drawn off = 9×512=4512=154HenceQuantity of   P remains in the mixtures after 9 litres is drawn off =7x−214Quantity of Q remains in the mixtures after 9   litres is drawn off =5x−154Since the container is filled with Q after 9 litres of mixture is drawn   off,Quantity of Q in the mixtures=5x−154+9=5x+214Given that the ratio of P and Q becomes 7 :   9⇒(7x−214):(5x+214)=7:9⇒(7x−214)(5x+214)=7963x−(9×214)=35x+(7×214)28x=(16×214)x=(16×214×28)   litres of P contained in the container initially = 7x=(7×16×214×28)=16×214×4=21   Answer : Option 21
<result>B</result>
A container contains a mixture of two liquids P and Q in the ratio 7 : 5. When 9 litres of mixture are
drawn off and the container is filled with Q, the ratio of P and Q becomes 7 : 9. How many litres of liquid
P was contained in the container initially?