Question

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 for writing 330 words on an average. How many words can be written using a bottle of ink containing one-fifth of a litre?

Answer 1

Length of the pen (h) = 7 cm

Radius of the pen (r) = `5/2` mm

= `5/(2 xx 10)` cm

= `1/4` cm

Volume of the barrel of a pen = Volume of the cylinder

= πr²h cu.units

= `22/7 xx 1/4 xx 1/4 xx 7  "cm"^3`

= `11/8  "cm"^3`

= `11/(8 xx 1000)` litre

For `11/8000` litre, writing words = 330

For `1/5` litre, No. of writing words

= `330 xx 1/5 ÷ 11/8000`

= `330/5 xx 8000/11`

= `(30 xx 8000)/5`

= 6 × 8000

= 48000 words

Number of words = 48000