200 logs are stacked in the following manner : 20 logs in the bottom row, 19 in the next row, 18 in the row next to it and so on (see Fig), in how many rows are the,200 logs placed and how many logs are in the top row ?

In a flower bed, there are 23 rose plants in the first row, 21 in the second, J9 in the third, and so on. There are 5 rose plants in the last row. How many rows are there,' in the flower bed?

In how many ways can 3 people be seated in a row containing 7 seats ?

In how many ways can 5 boys and 3 girls sit in a row so that no two girls are together ?

It is required to seat 5 men and 4 women in a row so that the women occupy the even places. How many such arrangements are possible ?

In how many ways can 4 boys and 3 girls be seated in a row so that no two girls are together ?

In how many ways can 5 girls be seated in a row so that two girls Ridhi and Sanya are never together?

A boat is to be manned by eight men, of whom 2 can only row on bow side and 1 can only row on stroke side; in how many ways can the crew be arranged?

Six X 's have to be placed in the squares of the figure below, such that each row contains atleast one X. in how many different ways can this be done?

Street Plan : A city has two main roads which cross each other at the centre of the city. These two roads are along the North-South direction and East-West direction. All other streets of the city run parallel to these roads and are 200 m apart. There are about 5 streets in each direction. Using 1 cm = 200 m, draw a model of the city on your notebook. Represent roads/ streets by single lines. There are many cross-streets in your model. A particular cross-street is made by two streets, one running in the North - South direction and another in the East - West direction. Each cross street is referred to in the following manner : the 2^(nd) street running in the North -South direction and 5^(th) in the East - West direction meet at some crossing, then we will call this crossstreet (2, 5). Using this convention find : how many cross-streets can be referred to as (4, 3).

Street Plan : A city has two main roads which cross each other at the centre of the city. These two roads are along the North-South direction and East-West direction. All other streets of the city run parallel to these roads and are 200 m apart. There are about 5 streets in each direction. Using 1 cm = 200 m, draw a model of the city on your notebook. Represent roads/ streets by single lines. There are many cross-streets in your model. A particular cross-street is made by two streets, one running in the North - South direction and another in the East - West direction. Each cross street is referred to in the following manner : the 2^(nd) street running in the North -South direction and 5^(th) in the East - West direction meet at some crossing, then we will call this crossstreet (2, 5). Using this convention find : how many cross-streets can be referred to as (3, 4).