☰
✕

Arithmetic Progressions
Question
Wired Faculty App

00 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. 5.2). In how many rows the 200 logs are placed and how many logs are in the top row?


Fig. 5.2.

Answer

In the bottom row = 20 logs
In the next row = 19 logs
In the row next to it = 18 logs and so on.
Thus, 20, 19, 18,... form an A .P. with
a1 = 20, a2 = 19, a3 = 18
Here d = 19 – 20 = (–1)
and Sn = 200

Hence, the required number of rows are 16 and in the top row there are 5 logs.

Sponsor Area

Some More Questions From Arithmetic Progressions Chapter

Write first four terms of the AP, when the first term a and the common difference d are given as follows:
a = –2, d = 0

Write first four terms of the AP, when the first term a and the common difference d are given as follows:
a = 4, d = – 3

Write first four terms of the AP, when the first term a and the common difference d are given as follows:

a = – 1.25, d = – 0.25

For the following APs, write the first term and the common difference
3, 1, – 1, – 3, . . .

For the following APs, write the first term and the common difference
– 5, – 1, 3, 7, . . .

For the following APs, write the first term and the common difference
0.6, 1.7, 2.8, 3.9, . . .