A cistern of capacity 8000 litres measures externally 3.3 m by 2.6 m by 1.2 m and its walls are 5 cm thick. The thickness of the bottom is:  Choose the correct choice from the following choices:
A) 90 cm B) 2 dm C) 1 m D) 1.1 cm E) None of these
Explanation:   Let the thickness of the bottom be x cm.   Then , [(330 - 10) × (260 - 10) × (120 - x)] = 8000 × 1000   =&gt; 320 × 250 × (120 - x) = 8000 × 1000   =&gt; (120 - x) = 8000×1000/320=   100   =&gt; x = 20 cm = 2 dm.   Answer: 2 dm
<result>B</result>
A cistern of capacity 8000 litres measures externally 3.3 m by 2.6 m by 1.2 m and its walls are 5 cm thick. The thickness of the bottom is: