A cistern of capacity 8000 litres measures externally 3.3 m by 2.6 m by 1.1 m and its walls are 5 cm thick. The thickness of the bottom is:

Let the thickness of the bottom be x cm.

Then, [(330 - 10) x (260 - 10) x (110 - x)] = 8000 x 1000

 320 x 250 x (110 - x) = 8000 x 1000

(110 - x) =	8000 x 1000	= 100
	320 x 250

 x = 10 cm = 1 dm.