Question

300 wooden logs are stacked such that there are 24 logs are in the bottom row, 23 in the next row, 22 in the row next to it and so on. In how many rows are 300 logs placed and how many logs are in the top row?

Answer 1

Sn = 300
a=24
d=-1
Sn=n/2[2a+(n-1)d]
300 =n/2[48+(n-1)-1]
600=49n-n^2
n^2-49n+600=0
n^2-25n-24n+600=0
n(n-25)-24(n-25)=0
(n-25)(n-24)=0
Therefore n=24 on=25
There are 24 or 25 rows of logs.
In the top row there is only one log.
An=a+(n-1)d
=24-23=1