Question 65463
Let the volume of the tank be V cu. in
Present volume of water = 1/4 th of the tank
                        = (1/4)V
Volume of water added = 10,000 cu. in

Now the volume of water in the tank = 2/3 rd of the tank
                                     = (2/3)V


==> (2/3)V  - (1/4)V  = 10,000 
==> (5/12) V = 10,000 [taking 12 as the LCD and adding]
==> V = 10,000 * (12/5) [multiplying by (12/5 on both the sides]
==> V = 24,000 

The volume of the tank = 24,000 cu. in

Good Luck!!!