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?

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 ?

Aman saves $320 during the first year, $ 360 in the second year, $ 400 in the third year and so on. In how many years will he save $ 20,000 ?

An inventor of the chess board suggested a reward of one grain of wheat for first square, 2 grains for the second, 4 grains for the third, and so on, doubling the amount of the grains for subsequent squares. How many grains would have to be given to the inventor ? (There are 64 squares in the chess board).

In how many ways can 6 girls and 4 boys be seated 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 ?

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

Balls are arranged in rows to form an equilateral triangle. The first row consists of one ball, the second row of two balls and so on. If 669 more balls are added,then all the balls can be arranged in the shape of a square and each of the sides, then contains 8 balls less than each side of the triangle. Determine the initial number of balls.

A family consists of a grandfather, 5 sons and daughters and 8 grand child. They are to be seated in a row for dinner. The grand children wish to occupy the 4 seats at each end and the grandfather refuses to have a grandchild on either side of him. In how many ways can the family be made to sit?