Solution: 

The numbers of logs in each row are in the form of an A.P. as 20, 19, 18,…

For the provided A.P.,

The first term, a = 20 and the common difference, d = a₂−a₁ = 19−20 = −1

Let for a total of 200 logs to be arranged in n rows.

Thus, S_n = 200

Using the sum of the nth term formula,

S_n = n/2 [2a +(n -1)d]

S₁₂ = 12/2 [2(20)+(n -1)(-1)]

400 = n (40−n+1)

400 = n (41-n)

400 = 41n−n²

n²−41n + 400 = 0

n²−16n−25n+400 = 0

n(n −16)−25(n −16) = 0

(n −16)(n −25) = 0

Either (n −16) = 0 or n−25 = 0

n = 16 or n = 25

Using the nth term formula,

a_n = a+(n−1)d

a₁₆ = 20+(16−1)(−1)

a₁₆ = 20−15

a₁₆ = 5

The 25^th term in the same way could be written as;

a₂₅ = 20+(25−1)(−1)

a₂₅ = 20−24

= −4

Because the numbers cannot be negative, the number of logs in the 16th row is 5..

As a result, 200 logs can be arranged in 16 rows, with 5 logs in the 16th row.