A cistern of capacity 8000 litres measures externally 3.3 m by 2.6 m by 1.3 m and its walls are 5 cm thick. The thickness of the bottom is:  Choose the correct answer
A) 90 cm  B) 3 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) × (130 - x)] = 8000 × 1000   =&gt; 320 × 250 × (130 - x) = 8000 × 1000   =&gt; (130 - x) = 8000×1000/320=   100   =&gt; x = 30 cm = 3 dm.   Answer: 3 dm
<result>B</result>
A cistern of capacity 8000 litres measures externally 3.3 m by 2.6 m by 1.3 m and its walls are 5 cm thick. The thickness of the bottom is: