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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?
Solution
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
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