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 pen will be used up on writing 330 words on an average. How many words would use up a bottle of ink containing one fifth of a litre?

                                 
Diameter of the barrel of the fountain pen = 5 mm = 0.5 cm ⇒ Radius of the barrel of the fountain pen = 0.25 cm
Volume of the barrel of the fountain pen = π r²h
                                                     = × 0.25 × 0.25 × 7
                                                     = 1.375 cu. cm ⇒ 1.375 cu. cm of ink writes 330 words on an average. ∴ One-fifth of a litre =× 1000 = 200 cu. cm ∴ Number of words 200 cu. cm of ink writes on an average = 200 ×
                                                      = 48000
The bottle of ink containing one-fifth of a litre of ink writes 48000 words on an average.