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)

  $\frac{Remaining Quantity}{Initial Quantity}=1-\frac{Replaced Quantity}{Total Quantity}$

(for petrol)    $\frac{2}{3}=1-\frac{10}{k}$

 => K = 30

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