Question

a cuboidal fish tank of lenght 30 cm breadth 20 cm and height 20 cm. the tank is placed on a horizontal table and it is three quarters full of water. Find the area of the tank which is in contact with water.

Answer 1

Length =30, breadth =20 and height =20 so, volume of tank=30x20x20=12000cm cube now vol of water=3/4 of vol of cuboid so vol of water=3/4 x 12000=9000cm cube so 30x20xh=9000 so h=15cm so dimension of tank which are in contact with water are:length =30, breadth =20 and height =15....so area if tank which is in contact with water = LSA of tank + area of base of tank. So.. =2(L+B)xH + LxB =2(30+20)x15+30x15 =2100cm square..... I hope this is the answer

Answer 2

Cuboidal fish tank:
   Length L = 30 cm.   Breadth = B = 20 cm.    Height = H = 20 cm
   
If the tank is 3/4 th full of water, it means that it is filled up to 3/4th of its height. So water is filled upto  h = 20 cm * 3/4 = 15 cm.

Surface area of the floor of the tank = L * B = 30 * 20 = 600 cm²
Surface area of the walls of the tank up to height = h = 15 cm:
           = 2 L h  + 2 B h
           = 2 * 30 cm * 15 cm + 2 * 20 cm * 15 cm
           = 1500 cm²

Total area in contact with water = 600 + 1500 = 2, 100 cm²