 Hello and welcome to the session. In this session we discuss the following question which says, the barrel of a fountain pen, cylindrical in shape, is 7 cm long and 3 cm in radius. A full barrel of ink in the pen will be used up in writing 198 words on an average. How many words would use up a bottle of ink containing one-fifth of a litter? First we shall recall the formula to find the volume of a cylinder. This is equal to pi r square h. Here we have r is the radius of the base of the cylinder, h is the height of the cylinder. This is the key idea for this question. Now we move on to the solution. Now the height of the barrel say h is given as 7 cm, is given in the question that the barrel is of the cylindrical shape. Then we have the radius of the barrel say r is given as 3 cm. Next we find out the volume of the barrel say v is given as pi r square h. So this is equal to pi into 3 square into 7 cm cube. This is equal to 22 upon 7 into 9 into 7 cm cube. 7 7 cancels and this is equal to 198 cm cube is the volume of the barrel. In the question we have that a full barrel of ink in the pen will be used up in writing 198 words on an average. That is we say that 198 cm cube is used for writing 198 words. Now we know that 1 liter is equal to 1000 cm cube. In the question we are asked to find out that how many words would use up a bottle of ink containing one-fifth of a liter. So one-fifth of a liter means one-fifth of 1000 cm cube. So let's find out that how many words would use up one-fifth of the liter of the ink. So 1 upon 5 into 1000 cm cube will be used for writing 198 upon 198 into 1 upon 5 into 1000 words. 198 cancels and 5 200 times is 1000. So this comes out to be equal to 200 words. So one-fifth of a liter of the ink will be used for writing 200 words. So 200 words is our final answer. Let's complete the session. Hope you have understood the solution for this question.