Given
Ratio of liquids A and B in jar = 4 : 1
After addition of liquid B the ratio become = 2 : 3
Calculation
Initially (A : B) = 4 : 1 --(1)
Final (A : B) = 2 : 3 ---(2)
In both condition the amount of A is same
So, eq (2) multiplied by 2
Final (A : B) = 4 : 6
change in B = 10 L
⇒ 6x - x = 10
⇒ x = 2
So Total liquid in jar = 10x = 20 litres
then Amount of A in jar(initially) = 20/5 × 4 = 16 litres
∴ the required answer is 16 litres

Alternate Method
Let liquid B in the mixture be x
liquid A in the mixture= 4x
amount of liquid A in 10-litre mixture = (4/5) × 10 = 8 litre
amount of liquid B in 10 litres of mixture=10–8= 2 litre
So, the remaining amount of liquid A and B in the mixture 4x-8, x-2 litre
After adding 10 litres of liquid B to the mixture the ratio of the amount of A and B
= (4x-8)/(x-2+10) =(4x-8)/(x+8) = 2/3
=> 12x - 24 = 2x + 16 => 12x - 2x = 16 + 24
=> 10x = 40 => x = 40/10= 4 lit
amount of liquid A in the mixture
= 4x = 4 × 4=16 litre