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. 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, 19 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 5 girls and 3 boys be selected in a row so that no two boys are together ?

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

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

If n objects are arrange in a row, then the number of ways of selecting three of these objects so that no two of them are next to each other is

(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 the other streets of the city run parallel to these roads and are 200m apart. There are 5 streets in each direaction. Using 1 cm =200cm, draw a model of teh city on your note book. Represent the 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 directin and another in the East-West direction. Each cross street is rreferred to in the following manner, If the 2 ^(nd) steeet running in teh North-South direction 5 ^(th) in the East-West direction meet at some crossing, then we will call this cross-street (2,5). Using this convection, find: How many cross-streets can be referred at 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 the other streets of the city run parallel to these roads and are 200m apart. There are 5 streets in each direaction. Using 1 cm =200cm, draw a model of teh city on your note book. Represent the 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 directin and another in the East-West direction. Each cross street is rreferred to in the following manner, If the 2 ^(nd) steeet running in teh North-South direction 5 ^(th) in the East-West direction meet at some crossing, then we will call this cross-street (2,5). Using this convection, find: How many cross-streets can be referred to as (3,4)