The ratio of petrol and kerosene in the container is 3:2 when 10 liters of the mixture is taken out and is replaced by the kerosene, the ratio become 2:3. Then total quantity of the mixture in the container is:

pool : kerosene 

   3  :  2(initially) 

   2  :  3(after replacement)

  R e m a i n i n g Q u a n t i t y I n i t i a l Q u a n t i t y = 1 - R e p l a c e d Q u a n t i t y T o t a l Q u a n t i t y

(for petrol)    2 3 = 1 - 10 k

 => K = 30

 Therefore the total quantity of the mixture in the container is 30 liters.