A can contains a mixture of two liquids A and B in the ratio 7 : 5. When 9 litres of mixture are drawn off and the can is filled with B, the ratio of A and B becomes
7 : 9. How many litres of liquid A was contained by the can initially?
Options.
A) 25
B) 21
C) 20
D) 10
E) 15

Rationale: suppose the can initially contains 7 x and 5 x litres mixtures a and b respectively quantity of a in mix . left = [ 7 x – 7 / 12 * 9 ] = [ 7 x – 21 / 4 ] quantity of b in mix . left = [ 5 x – 5 / 12 * 9 ] = [ 5 x - 15 / 4 ] therefore [ 7 x - 21 / 4 ] = 7 / 9 or 28 x - 21 = 7 / 9 [ 5 x - 15 / 4 ] + 9 20 x + 21 252 x - 189 = 140 x + 147 or 112 x = 336 , x = 3 . quantity of a in the can initially = 7 * 3 = 21 answer : b
Answer: B