A cistern of capacity 8000 litres measures externally 3.3

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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 :

1. 1 m
2. 1.1 m
3. 1 dm
4. 90 cm

Correct Option: C

Walls are 5 cm thick.
∴ Internal length = (330 – 2 × 5) cm = 320 cm.
Let the thickness of bottom be x Breadth = (260 – 10)cm
= 250 cm Height = (110 – x) cm
Here, the cistern is assumed to be open and x is the thickness of bottom.
∴ 320 × 250 × (110 – x) = 8000 litres
⇒ 320 × 250 × (110 – x) = 8000 × 1000 cm³

⇒ (110 - x) =	8000000
	320 × 250

⇒ 110 – x = 100
⇒ x = 10 cm or 1 dm.