A vessel contains a solution of two liquids A and B in the ratio 5 : 3. When 10 litres of the solution is taken out and replaced by the same quantity of B, the ratio of A and B in the vessel becomes 10 : 11. The quantity (in litres) of the solution, in the vessel was ______.

42

The ratio of two liquids 

 A : B = 5 : 3 or 10 : 6,

⇒        A   :   B

Initial  10 :   6

After   10 :   11

⇒ After B - Initial B = 10 litres,

⇒ (11 - 6)x = 10L

⇒ 5x = 10L

⇒ x = 2,

Hence quantity of solution in vessel = (10 + 11) x 2 = 21 x 2 = 42 litres,