The barrel of a fountain pen, cylindrical in shape, is 7 cm long and 5 mm in diameter.

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Let us first calculate the volume of barrel of pen that is of cylindrical shape

Consider barrel,

Since 1cm = 10 mm

Base diameter = 5 mm = 0.5 cm

Base radius, r = 0.25 cm

Height, h = 7 cm

We know that,

Volume of a cylinder = πr²h

Volume of barrel = π (0.25)²7

Volume of barrel = 22/7 × 0.25 × 0.25 × 7 = 1.375 cm³

Hence, according to the question,

1.375 cm³ of ink can write 3300 words

No of words that can be written by 1 cm³ of ink = 3300/1.375 = 2400 words

1/5^th of a liter = 0.2 L

We know that,

1 L = 1000 cm³

0.2 L = 200 cm³

So, no of words that can be written by 200 cm³ = 2400(200) = 480000 words

Therefore, 1/5^th of a liter ink can write 480000 words.