The barrel of a fountain pen, cylindrical in shape, is 7 cm long and 5 mm in diameter. A full barrel of ink in the pin is used up on writing 3300 words on an average. How many words can be written in a bottle of ink containing one-fifth of a Litre?
Let us first calculate the volume of barrel of pen that is of cylindrical shape
For barrel,
Base diameter = 5 mm = 0.5 cm [As 1 cm = 10 mm]
Base radius, r = 0.25 cm
[as radius = diameter/2]
Height, h = 7 cm
As we know,
Volume of a cylinder = πr2h
Where r is base radius and h is the height of cylinder
volume of barrel
⇒ Volume of barrel
So,
1.375 cm3 of ink can write 3300 words
No of words that can be written by 1 cm^3
[ Also 
of a liter i.e. 0.2 L and we know
1 L = 1000 cm3
0.2 L = 200 cm3 ]
No of words that can be written by 200 cm3 = 2400(200) = 480000 words
So,
One-fifth of a liter ink can write 480000 words on an average.